diff --git a/Retroactiune.Core/Entities/Feedback.cs b/Retroactiune.Core/Entities/Feedback.cs
index 1e1c181..3475e58 100644
--- a/Retroactiune.Core/Entities/Feedback.cs
+++ b/Retroactiune.Core/Entities/Feedback.cs
@@ -10,28 +10,23 @@ namespace Retroactiune.Core.Entities
     /// </summary>
     public class Feedback
     {
-        private uint _rating;
 
+        public Feedback()
+        {
+            Id = ObjectId.GenerateNewId().ToString();
+            CreatedAt = DateTime.UtcNow;
+        }
+        
         [BsonId, JsonPropertyName("id")]
         [BsonRepresentation(BsonType.ObjectId)]
         public string Id { get; set; }
 
+        [JsonPropertyName("feedback_receiver_id")]
+        [BsonRepresentation(BsonType.ObjectId)]
+        public string FeedbackReceiverId { get; set; }
+        
         [JsonPropertyName("rating")]
-        public uint Rating
-        {
-            get => _rating;
-            set
-            {
-                if (value <= 5)
-                {
-                    _rating = value;
-                }
-                else
-                {
-                    throw new ArgumentException();
-                }
-            }
-        }
+        public uint Rating { get; set; }
 
         [JsonPropertyName("description")] public string Description { get; set; }
 
diff --git a/Retroactiune.Core/Entities/FeedbackReceiver.cs b/Retroactiune.Core/Entities/FeedbackReceiver.cs
index 6980ea3..9245bcd 100644
--- a/Retroactiune.Core/Entities/FeedbackReceiver.cs
+++ b/Retroactiune.Core/Entities/FeedbackReceiver.cs
@@ -11,6 +11,12 @@ namespace Retroactiune.Core.Entities
     /// </summary>
     public class FeedbackReceiver
     {
+        public FeedbackReceiver()
+        {
+            Id = ObjectId.GenerateNewId().ToString();
+            CreatedAt = DateTime.UtcNow;
+        }
+        
         [BsonId, JsonPropertyName("id")]
         [BsonRepresentation(BsonType.ObjectId)]
         public string Id { get; set; }
diff --git a/Retroactiune.Core/Entities/Token.cs b/Retroactiune.Core/Entities/Token.cs
index 90f75ae..702d182 100644
--- a/Retroactiune.Core/Entities/Token.cs
+++ b/Retroactiune.Core/Entities/Token.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Runtime.CompilerServices;
 using System.Text.Json.Serialization;
+using Ardalis.GuardClauses;
 using MongoDB.Bson;
 using MongoDB.Bson.Serialization.Attributes;
 
@@ -12,6 +13,13 @@ namespace Retroactiune.Core.Entities
     /// </summary>
     public class Token
     {
+
+        public Token()
+        {
+            Id = ObjectId.GenerateNewId().ToString();
+            CreatedAt = DateTime.UtcNow;
+        }
+        
         [BsonId, JsonPropertyName("id")]
         [BsonRepresentation(BsonType.ObjectId)]
         public string Id { get; set; }
@@ -41,5 +49,14 @@ namespace Retroactiune.Core.Entities
         {
             return RuntimeHelpers.GetHashCode(this);
         }
+
+        public bool IsValid(FeedbackReceiver feedbackReceiver)
+        {
+            Guard.Against.Null(feedbackReceiver, nameof(feedbackReceiver));
+            var hasExpired = ExpiryTime != null && ExpiryTime <= DateTime.UtcNow;
+            var differentFeedbackReceiver = !FeedbackReceiverId.Equals(feedbackReceiver.Id);
+            var isUsed = TimeUsed != null;
+            return !(hasExpired || differentFeedbackReceiver || isUsed);
+        }
     }
 }
\ No newline at end of file
diff --git a/Retroactiune.Core/Interfaces/IFeedbacksService.cs b/Retroactiune.Core/Interfaces/IFeedbacksService.cs
new file mode 100644
index 0000000..fc124d1
--- /dev/null
+++ b/Retroactiune.Core/Interfaces/IFeedbacksService.cs
@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using Retroactiune.Core.Entities;
+
+namespace Retroactiune.Core.Interfaces
+{
+    public interface IFeedbacksService
+    {
+
+        /// <summary>
+        /// Adds Feedback to a FeedbackReceiver.
+        /// </summary>
+        /// <param name="feedback">The feedback.</param>
+        /// <param name="receiver">The feedback receiver.</param>
+        /// <returns></returns>
+        public Task AddFeedbackAsync(Feedback feedback, FeedbackReceiver receiver);
+    }
+}
\ No newline at end of file
diff --git a/Retroactiune.Core/Interfaces/ITokensService.cs b/Retroactiune.Core/Interfaces/ITokensService.cs
index f57d37f..5518d0b 100644
--- a/Retroactiune.Core/Interfaces/ITokensService.cs
+++ b/Retroactiune.Core/Interfaces/ITokensService.cs
@@ -23,14 +23,14 @@ namespace Retroactiune.Core.Interfaces
         /// </summary>
         /// <param name="tokenIds">A list of tokens to delete.</param>
         /// <returns>The result of the delete operation.</returns>
-        public Task DeleteTokens(IEnumerable<string> tokenIds);
+        public Task DeleteTokensAsync(IEnumerable<string> tokenIds);
 
         /// <summary>
-        /// List and filters tokens.
+        /// Finds and filters tokens.
         /// </summary>
         /// <param name="filters">Filters object for filtering results.</param>
         /// <returns>A list of tokens matching the filters.</returns>
-        public Task<IEnumerable<Token>> ListTokens(TokenListFilters filters);
+        public Task<IEnumerable<Token>> FindAsync(TokenListFilters filters);
 
         /// <summary>
         /// Deletes tokens, by their associated FeedbackReceiverId.
@@ -38,5 +38,11 @@ namespace Retroactiune.Core.Interfaces
         /// <param name="feedbackReceiverIds">A list of FeedbackReceiverIDs.</param>
         /// <returns>The result of the delete operation.</returns>
         public Task DeleteManyByFeedbackReceiverIdAsync(IEnumerable<string> feedbackReceiverIds);
+        
+        /// <summary>
+        /// Marks the token as being used.
+        /// </summary>
+        /// <param name="token">The token.</param>
+        public Task MarkTokenAsUsedAsync(Token token);
     }
 }
\ No newline at end of file
diff --git a/Retroactiune.Core/Retroactiune.Core.csproj b/Retroactiune.Core/Retroactiune.Core.csproj
index 02f0260..792b4db 100644
--- a/Retroactiune.Core/Retroactiune.Core.csproj
+++ b/Retroactiune.Core/Retroactiune.Core.csproj
@@ -5,6 +5,7 @@
     </PropertyGroup>
 
     <ItemGroup>
+      <PackageReference Include="Ardalis.GuardClauses" Version="3.2.0" />
       <PackageReference Include="MongoDB.Driver" Version="2.12.3" />
     </ItemGroup>
 
diff --git a/Retroactiune.Core/Services/FeedbacksService.cs b/Retroactiune.Core/Services/FeedbacksService.cs
new file mode 100644
index 0000000..6020956
--- /dev/null
+++ b/Retroactiune.Core/Services/FeedbacksService.cs
@@ -0,0 +1,29 @@
+using System.Threading.Tasks;
+using Ardalis.GuardClauses;
+using MongoDB.Driver;
+using Retroactiune.Core.Entities;
+using Retroactiune.Core.Interfaces;
+
+namespace Retroactiune.Core.Services
+{
+    public class FeedbacksService : IFeedbacksService
+    {
+        private readonly IMongoCollection<Feedback> _collection;
+
+        public FeedbacksService(IMongoClient client, IDatabaseSettings settings)
+        {
+            var database = client.GetDatabase(settings.DatabaseName);
+            _collection = database.GetCollection<Feedback>(settings.FeedbackCollectionName); 
+        }
+        
+        public async Task AddFeedbackAsync(Feedback feedback, FeedbackReceiver receiver)
+        {
+            // TODO: Unit test.
+            Guard.Against.Null(feedback, nameof(feedback));
+            Guard.Against.Null(receiver, nameof(receiver));
+
+            feedback.FeedbackReceiverId = receiver.Id;
+            await _collection.InsertOneAsync(feedback);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Retroactiune.Core/Services/TokensService.cs b/Retroactiune.Core/Services/TokensService.cs
index 5257e78..6ad22c4 100644
--- a/Retroactiune.Core/Services/TokensService.cs
+++ b/Retroactiune.Core/Services/TokensService.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
+using Ardalis.GuardClauses;
 using MongoDB.Driver;
 using Retroactiune.Core.Entities;
 using Retroactiune.Core.Interfaces;
@@ -21,10 +22,7 @@ namespace Retroactiune.Core.Services
         public async Task GenerateTokensAsync(int numberOfTokens, string feedbackReceiverGuid,
             DateTime? expiryTime = null)
         {
-            if (numberOfTokens <= 0)
-            {
-                throw new ArgumentException("numberOfTokens must be positive");
-            }
+            Guard.Against.Negative(numberOfTokens, nameof(numberOfTokens));
 
             var token = new List<Token>();
             for (var i = 0; i < numberOfTokens; i++)
@@ -41,7 +39,7 @@ namespace Retroactiune.Core.Services
             await _collection.InsertManyAsync(token);
         }
 
-        public async Task DeleteTokens(IEnumerable<string> tokenIds)
+        public async Task DeleteTokensAsync(IEnumerable<string> tokenIds)
         {
             try
             {
@@ -54,7 +52,7 @@ namespace Retroactiune.Core.Services
             }
         }
 
-        public async Task<IEnumerable<Token>> ListTokens(TokenListFilters filters)
+        public async Task<IEnumerable<Token>> FindAsync(TokenListFilters filters)
         {
             var filterBuilder = new FilterDefinitionBuilder<Token>();
             var activeFilters = new List<FilterDefinition<Token>>();
@@ -119,5 +117,14 @@ namespace Retroactiune.Core.Services
                 throw new GenericServiceException($"Operation failed: {e.Message} {e.StackTrace}");
             }
         }
+
+        public async Task MarkTokenAsUsedAsync(Token token)
+        {
+            // TODO: Unit test.
+            var filterBuilder = new FilterDefinitionBuilder<Token>();
+            var updateBuilder = new UpdateDefinitionBuilder<Token>();
+            await _collection.UpdateOneAsync(filterBuilder.Eq(i => i.Id, token.Id),
+                updateBuilder.Set(i => i.TimeUsed, DateTime.UtcNow));
+        }
     }
 }
\ No newline at end of file
diff --git a/Retroactiune.UnitTests/Retroactiune.Core/Services/TestTokensService.cs b/Retroactiune.UnitTests/Retroactiune.Core/Services/TestTokensService.cs
index 001fec4..a69e1ea 100644
--- a/Retroactiune.UnitTests/Retroactiune.Core/Services/TestTokensService.cs
+++ b/Retroactiune.UnitTests/Retroactiune.Core/Services/TestTokensService.cs
@@ -68,16 +68,8 @@ namespace Retroactiune.Tests.Retroactiune.Core.Services
             await service.GenerateTokensAsync(3, "Hello", expiryTime);
 
             // Assert
-            var item = new Token
-            {
-                Id = null,
-                ExpiryTime = expiryTime,
-                TimeUsed = null,
-                FeedbackReceiverId = "Hello",
-                CreatedAt = expiryTime
-            };
             mongoCollectionMock.Verify(
-                i => i.InsertManyAsync(new[] {item, item, item},
+                i => i.InsertManyAsync(It.IsAny<IEnumerable<Token>>(),
                     It.IsAny<InsertManyOptions>(),
                     It.IsAny<CancellationToken>()), Times.Once);
         }
@@ -106,7 +98,7 @@ namespace Retroactiune.Tests.Retroactiune.Core.Services
 
             // Test
             var service = new TokensService(mongoClientMock.Object, mongoSettingsMock.Object);
-            await service.DeleteTokens(new[] {"test_id"});
+            await service.DeleteTokensAsync(new[] {"test_id"});
 
             // Assert
             mongoCollectionMock.Verify(
@@ -145,7 +137,7 @@ namespace Retroactiune.Tests.Retroactiune.Core.Services
 
             // Test
             var service = new TokensService(mongoClientMock.Object, mongoSettingsMock.Object);
-            var result = await service.ListTokens(new TokenListFilters());
+            var result = await service.FindAsync(new TokenListFilters());
 
             // Assert
             Assert.IsType<List<Token>>(result);
@@ -185,7 +177,7 @@ namespace Retroactiune.Tests.Retroactiune.Core.Services
 
             // Test
             var service = new TokensService(mongoClientMock.Object, mongoSettingsMock.Object);
-            var result = await service.ListTokens(new TokenListFilters
+            var result = await service.FindAsync(new TokenListFilters
             {
                 Ids = new[] {"a", "b"},
                 FeedbackReceiverId = "abc",
diff --git a/Retroactiune.UnitTests/Retroactiune.WebAPI/Controllers/TestFeedbackReceiverController.cs b/Retroactiune.UnitTests/Retroactiune.WebAPI/Controllers/TestFeedbackReceiverController.cs
index d159e05..624bac0 100644
--- a/Retroactiune.UnitTests/Retroactiune.WebAPI/Controllers/TestFeedbackReceiverController.cs
+++ b/Retroactiune.UnitTests/Retroactiune.WebAPI/Controllers/TestFeedbackReceiverController.cs
@@ -23,10 +23,12 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var mapper = TestUtils.GetMapper();
             var mockService = new Mock<IFeedbackReceiversService>();
             var tokensService = new Mock<ITokensService>();
+            var feedbacksService = new Mock<IFeedbacksService>();
             var logger = new Mock<ILogger<FeedbackReceiversController>>();
 
             // Test
-            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object, mapper, null,
+            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object,
+                feedbacksService.Object, mapper, null,
                 logger.Object);
             var result = await controller.Post(new List<FeedbackReceiverInDto>());
 
@@ -42,10 +44,12 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var mapper = TestUtils.GetMapper();
             var mockService = new Mock<IFeedbackReceiversService>();
             var tokensService = new Mock<ITokensService>();
+            var feedbacksService = new Mock<IFeedbacksService>();
             var logger = new Mock<ILogger<FeedbackReceiversController>>();
 
             // Test
-            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object, mapper, null,
+            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object,
+                feedbacksService.Object, mapper, null,
                 logger.Object);
             var result = await controller.Post(items);
 
@@ -61,10 +65,12 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var mapper = TestUtils.GetMapper();
             var mockService = new Mock<IFeedbackReceiversService>();
             var tokensService = new Mock<ITokensService>();
+            var feedbacksService = new Mock<IFeedbacksService>();
             var logger = new Mock<ILogger<FeedbackReceiversController>>();
 
             // Test
-            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object, mapper, null,
+            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object,
+                feedbacksService.Object, mapper, null,
                 logger.Object);
             var result = await controller.Delete("bad_guid_but_unit_test_works_cause_validation_doesnt");
 
@@ -84,10 +90,12 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var mapper = TestUtils.GetMapper();
             var mockService = new Mock<IFeedbackReceiversService>();
             var tokensService = new Mock<ITokensService>();
+            var feedbacksService = new Mock<IFeedbacksService>();
             var logger = new Mock<ILogger<FeedbackReceiversController>>();
 
             // Test
-            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object, mapper, null,
+            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object,
+                feedbacksService.Object, mapper, null,
                 logger.Object);
             var items = new[] {"bad_guid_but_unit_test_works_cause_validation_doesnt", "2", "3"};
             var result = await controller.DeleteMany(items);
@@ -106,12 +114,14 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var mapper = TestUtils.GetMapper();
             var mockService = new Mock<IFeedbackReceiversService>();
             var tokensService = new Mock<ITokensService>();
+            var feedbacksService = new Mock<IFeedbacksService>();
             var logger = new Mock<ILogger<FeedbackReceiversController>>();
             mockService.Setup(i => i.DeleteManyAsync(It.IsAny<IEnumerable<string>>()))
                 .ThrowsAsync(new GenericServiceException("op failed"));
 
             // Test
-            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object, mapper, null,
+            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object,
+                feedbacksService.Object, mapper, null,
                 logger.Object);
             var items = new[] {"bad_guid_but_unit_test_works_cause_validation_doesnt", "2", "3"};
             var result = await controller.DeleteMany(items);
@@ -129,12 +139,14 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var mapper = TestUtils.GetMapper();
             var mockService = new Mock<IFeedbackReceiversService>();
             var tokensService = new Mock<ITokensService>();
+            var feedbacksService = new Mock<IFeedbacksService>();
             var logger = new Mock<ILogger<FeedbackReceiversController>>();
             mockService.Setup(i => i.FindAsync(It.IsAny<IEnumerable<string>>(), null, null))
                 .ReturnsAsync(new[] {new FeedbackReceiver()});
 
             // Test
-            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object, mapper, null,
+            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object,
+                feedbacksService.Object, mapper, null,
                 logger.Object);
             var result = await controller.Get("bad_guid_but_unit_test_works_cause_validation_doesnt");
 
@@ -152,10 +164,12 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var mapper = TestUtils.GetMapper();
             var mockService = new Mock<IFeedbackReceiversService>();
             var tokensService = new Mock<ITokensService>();
+            var feedbacksService = new Mock<IFeedbacksService>();
             var logger = new Mock<ILogger<FeedbackReceiversController>>();
 
             // Test
-            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object, mapper, null,
+            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object,
+                feedbacksService.Object, mapper, null,
                 logger.Object);
             var result = await controller.Get("bad_guid_but_unit_test_works_cause_validation_doesnt");
 
@@ -173,11 +187,13 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var mapper = TestUtils.GetMapper();
             var mockService = new Mock<IFeedbackReceiversService>();
             var tokensService = new Mock<ITokensService>();
+            var feedbacksService = new Mock<IFeedbacksService>();
             var logger = new Mock<ILogger<FeedbackReceiversController>>();
             var filterArr = filter as string[] ?? filter.ToArray();
 
             // Test
-            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object, mapper, null,
+            var controller = new FeedbackReceiversController(mockService.Object, tokensService.Object,
+                feedbacksService.Object, mapper, null,
                 logger.Object);
             var result = await controller.List(filterArr, offset, limit);
 
diff --git a/Retroactiune.UnitTests/Retroactiune.WebAPI/Controllers/TestTokensController.cs b/Retroactiune.UnitTests/Retroactiune.WebAPI/Controllers/TestTokensController.cs
index 5d29719..0722866 100644
--- a/Retroactiune.UnitTests/Retroactiune.WebAPI/Controllers/TestTokensController.cs
+++ b/Retroactiune.UnitTests/Retroactiune.WebAPI/Controllers/TestTokensController.cs
@@ -74,7 +74,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
 
             // Assert
             Assert.IsType<NoContentResult>(result);
-            tokens.Verify(i => i.DeleteTokens(new[] {"my_guid"}), Times.Once);
+            tokens.Verify(i => i.DeleteTokensAsync(new[] {"my_guid"}), Times.Once);
         }
 
         [Fact]
@@ -85,7 +85,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var feedbackService = new Mock<IFeedbackReceiversService>();
             var tokens = new Mock<ITokensService>();
             var logger = new Mock<ILogger<TokensController>>();
-            tokens.Setup(i => i.DeleteTokens(It.IsAny<IEnumerable<string>>()))
+            tokens.Setup(i => i.DeleteTokensAsync(It.IsAny<IEnumerable<string>>()))
                 .Throws(new GenericServiceException("op fail"));
 
             // Test
@@ -94,7 +94,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
 
             // Assert
             Assert.IsType<BadRequestObjectResult>(result);
-            tokens.Verify(i => i.DeleteTokens(new[] {"my_guid"}), Times.Once);
+            tokens.Verify(i => i.DeleteTokensAsync(new[] {"my_guid"}), Times.Once);
         }
 
         [Fact]
@@ -112,7 +112,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
 
             // Assert
             Assert.IsType<NoContentResult>(result);
-            tokens.Verify(i => i.DeleteTokens(new[] {"my_guid", "b"}), Times.Once);
+            tokens.Verify(i => i.DeleteTokensAsync(new[] {"my_guid", "b"}), Times.Once);
         }
 
         [Fact]
@@ -123,7 +123,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var feedbackService = new Mock<IFeedbackReceiversService>();
             var tokens = new Mock<ITokensService>();
             var logger = new Mock<ILogger<TokensController>>();
-            tokens.Setup(i => i.DeleteTokens(It.IsAny<IEnumerable<string>>()))
+            tokens.Setup(i => i.DeleteTokensAsync(It.IsAny<IEnumerable<string>>()))
                 .Throws(new GenericServiceException("op fail"));
 
             // Test
@@ -132,7 +132,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
 
             // Assert
             Assert.IsType<BadRequestObjectResult>(result);
-            tokens.Verify(i => i.DeleteTokens(new[] {"my_guid", "b"}), Times.Once);
+            tokens.Verify(i => i.DeleteTokensAsync(new[] {"my_guid", "b"}), Times.Once);
         }
 
         [Fact]
@@ -150,7 +150,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             
             // Assert
             Assert.IsType<OkObjectResult>(result);
-            tokens.Verify(i => i.ListTokens(It.IsAny<TokenListFilters>()), Times.Once);
+            tokens.Verify(i => i.FindAsync(It.IsAny<TokenListFilters>()), Times.Once);
         }
         
         [Fact]
@@ -161,7 +161,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             var feedbackService = new Mock<IFeedbackReceiversService>();
             var tokens = new Mock<ITokensService>();
             var logger = new Mock<ILogger<TokensController>>();
-            tokens.Setup(i => i.ListTokens(It.IsAny<TokenListFilters>()))
+            tokens.Setup(i => i.FindAsync(It.IsAny<TokenListFilters>()))
                 .Throws(new GenericServiceException("op fail"));
 
             // Test
@@ -170,7 +170,7 @@ namespace Retroactiune.Tests.Retroactiune.WebAPI.Controllers
             
             // Assert
             Assert.IsType<BadRequestObjectResult>(result);
-            tokens.Verify(i => i.ListTokens(It.IsAny<TokenListFilters>()), Times.Once);
+            tokens.Verify(i => i.FindAsync(It.IsAny<TokenListFilters>()), Times.Once);
         }
     }
 }
\ No newline at end of file
diff --git a/Retroactiune.WebAPI/Controllers/FeedbackController.cs b/Retroactiune.WebAPI/Controllers/FeedbackController.cs
deleted file mode 100644
index 1d7e1f1..0000000
--- a/Retroactiune.WebAPI/Controllers/FeedbackController.cs
+++ /dev/null
@@ -1,9 +0,0 @@
-using Microsoft.AspNetCore.Mvc;
-
-namespace Retroactiune.Controllers
-{
-    public class FeedbackController : ControllerBase
-    {
-        // TODO Add feedback, list feedback, delete feedback, ged feedback.
-    }
-}
\ No newline at end of file
diff --git a/Retroactiune.WebAPI/Controllers/FeedbackReceiversController.cs b/Retroactiune.WebAPI/Controllers/FeedbackReceiversController.cs
index 340c3d4..0b519d3 100644
--- a/Retroactiune.WebAPI/Controllers/FeedbackReceiversController.cs
+++ b/Retroactiune.WebAPI/Controllers/FeedbackReceiversController.cs
@@ -1,5 +1,4 @@
-using System;
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.Linq;
 using System.Threading.Tasks;
@@ -24,15 +23,17 @@ namespace Retroactiune.Controllers
         // Note: Probably refactor this to use an Aggregate object, need to learn more about aggregates..
         private readonly IFeedbackReceiversService _feedbackReceiversService;
         private readonly ITokensService _tokensService;
+        private readonly IFeedbacksService _feedbacksService;
         private readonly IMapper _mapper;
         private readonly ILogger _logger;
 
         public FeedbackReceiversController(IFeedbackReceiversService feedbackReceiversService,
-            ITokensService tokensService, IMapper mapper,
+            ITokensService tokensService, IFeedbacksService feedbacksService, IMapper mapper,
             IOptions<ApiBehaviorOptions> apiBehaviorOptions, ILogger<FeedbackReceiversController> logger)
         {
             _feedbackReceiversService = feedbackReceiversService;
             _tokensService = tokensService;
+            _feedbacksService = feedbacksService;
             _mapper = mapper;
             _apiBehaviorOptions = apiBehaviorOptions;
             _logger = logger;
@@ -59,12 +60,7 @@ namespace Retroactiune.Controllers
                 return _apiBehaviorOptions?.Value.InvalidModelStateResponseFactory(ControllerContext);
             }
 
-            var mappedItems = feedbackReceiversDto.Select(i =>
-            {
-                var result = _mapper.Map<FeedbackReceiver>(i);
-                result.CreatedAt = DateTime.UtcNow;
-                return result;
-            });
+            var mappedItems = feedbackReceiversDto.Select(i => _mapper.Map<FeedbackReceiver>(i));
 
             await _feedbackReceiversService.CreateManyAsync(mappedItems);
 
@@ -171,5 +167,57 @@ namespace Retroactiune.Controllers
                 });
             }
         }
+
+        /// <summary>
+        /// Add Feedback to a FeedbackReceiver.
+        /// </summary>
+        /// <param name="guid">The guid of the FeedbackReceiver to add feedback.</param>
+        /// <param name="feedbackInDto">The feedback dto.</param>
+        /// <response code="200">The feedback has been added.</response>
+        /// <response code="404">The request is invalid.</response>  
+        /// <returns></returns>
+        [HttpPost("{guid}/feedbacks")]
+        [ProducesResponseType(typeof(NoContentResult), StatusCodes.Status204NoContent)]
+        [ProducesResponseType(typeof(BasicResponse), StatusCodes.Status400BadRequest)]
+        public async Task<IActionResult> AddFeedback(string guid, [FromBody] FeedbackInDto feedbackInDto)
+        {
+            // TODO: Unit & integration test.
+            var receivers = await _feedbackReceiversService.FindAsync(new[] {guid}, limit: 1);
+            var tokenEnum = await _tokensService.FindAsync(new TokenListFilters
+            {
+                Ids = new[] {feedbackInDto.TokenId}
+            });
+            var feedbackReceivers = receivers as FeedbackReceiver[] ?? receivers.ToArray();
+            var tokens = (tokenEnum as Token[] ?? tokenEnum.ToArray());
+            if (!feedbackReceivers.Any())
+            {
+                return BadRequest(new BasicResponse
+                {
+                    Message = $"FeedbackReceiver with id {guid} not found."
+                });
+            }
+
+            if (tokens.Length == 0)
+            {
+                return BadRequest(new BasicResponse
+                {
+                    Message = "Token not found."
+                });
+            }
+
+            var token = tokens[0];
+            if (!token.IsValid(feedbackReceivers[0]))
+            {
+                return BadRequest(new BasicResponse
+                {
+                    Message = "Token is invalid."
+                });
+            }
+
+            var feedback = _mapper.Map<Feedback>(feedbackInDto);
+            await Task.WhenAll(_tokensService.MarkTokenAsUsedAsync(token),
+                _feedbacksService.AddFeedbackAsync(feedback, feedbackReceivers[0]));
+            return Ok();
+        }
     }
 }
\ No newline at end of file
diff --git a/Retroactiune.WebAPI/Controllers/TokensController.cs b/Retroactiune.WebAPI/Controllers/TokensController.cs
index d12a116..a50a5e7 100644
--- a/Retroactiune.WebAPI/Controllers/TokensController.cs
+++ b/Retroactiune.WebAPI/Controllers/TokensController.cs
@@ -45,7 +45,7 @@ namespace Retroactiune.Controllers
             try
             {
                 var tokenFilters = _mapper.Map<TokenListFilters>(filtersDto);
-                var response = await _tokensService.ListTokens(tokenFilters);
+                var response = await _tokensService.FindAsync(tokenFilters);
                 return Ok(response);
             }
             catch (GenericServiceException e)
@@ -104,7 +104,7 @@ namespace Retroactiune.Controllers
         {
             try
             {
-                await _tokensService.DeleteTokens(tokenIds);
+                await _tokensService.DeleteTokensAsync(tokenIds);
                 return NoContent();
             }
             catch (GenericServiceException e)
@@ -133,7 +133,7 @@ namespace Retroactiune.Controllers
         {
             try
             {
-                await _tokensService.DeleteTokens(new[] {guid});
+                await _tokensService.DeleteTokensAsync(new[] {guid});
                 return NoContent();
             }
             catch (GenericServiceException e)
diff --git a/Retroactiune.WebAPI/DataTransferObjects/FeedbackInDto.cs b/Retroactiune.WebAPI/DataTransferObjects/FeedbackInDto.cs
index 63c7ca0..5e53702 100644
--- a/Retroactiune.WebAPI/DataTransferObjects/FeedbackInDto.cs
+++ b/Retroactiune.WebAPI/DataTransferObjects/FeedbackInDto.cs
@@ -1,5 +1,4 @@
-using System;
-using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations;
 
 namespace Retroactiune.DataTransferObjects
 {
@@ -8,27 +7,12 @@ namespace Retroactiune.DataTransferObjects
     /// </summary>
     public class FeedbackInDto
     {
-        private uint _rating;
-
-        [Required, StringLength(24, ErrorMessage = "invalid guid, must be 24 characters", MinimumLength = 24)]
-        public string FeedbackReceiverId { get; set; }
-
-        [Required]
-        public uint Rating
-        {
-            get => _rating;
-            set
-            {
-                if (value <= 5)
-                {
-                    _rating = value;
-                }
-                else
-                {
-                    throw new ArgumentException();
-                }
-            }
-        }
+        
+        [Required, StringLength(24, ErrorMessage = "invalid guid, must be 24 characters", MinimumLength = 24)] 
+        public string TokenId { get; set; }
+        
+        [Required, Range(0, 5, ErrorMessage = "The rating is out of range. [0-5]")]
+        public uint Rating { get; set; }
 
         [Required] public string Description { get; set; }
     }
diff --git a/Retroactiune.WebAPI/MappingProfile.cs b/Retroactiune.WebAPI/MappingProfile.cs
index c3e5a07..0f9a54a 100644
--- a/Retroactiune.WebAPI/MappingProfile.cs
+++ b/Retroactiune.WebAPI/MappingProfile.cs
@@ -12,6 +12,7 @@ namespace Retroactiune
             CreateMap<ListTokensFiltersDto, TokenListFilters>();
             CreateMap<FeedbackReceiver, FeedbackReceiverInDto>().ReverseMap();
             CreateMap<FeedbackReceiver, FeedbackReceiverOutDto>();
+            CreateMap<FeedbackInDto, Feedback>();
         }
     }
 }
\ No newline at end of file
diff --git a/Retroactiune.WebAPI/Startup.cs b/Retroactiune.WebAPI/Startup.cs
index 61a5e6a..c877a75 100644
--- a/Retroactiune.WebAPI/Startup.cs
+++ b/Retroactiune.WebAPI/Startup.cs
@@ -40,6 +40,7 @@ namespace Retroactiune
             // Services
             services.AddSingleton<IFeedbackReceiversService, FeedbackReceiversService>();
             services.AddSingleton<ITokensService, TokensService>();
+            services.AddSingleton<IFeedbacksService, FeedbacksService>();
             services.AddSingleton<IMongoClient, MongoClient>(i =>
             {
                 var settings = i.GetService<IOptions<DatabaseSettings>>();
diff --git a/Retroactiune.WebAPI/TestingStartup.cs b/Retroactiune.WebAPI/TestingStartup.cs
index 0a3b32d..b33feaf 100644
--- a/Retroactiune.WebAPI/TestingStartup.cs
+++ b/Retroactiune.WebAPI/TestingStartup.cs
@@ -36,6 +36,7 @@ namespace Retroactiune
             // Services
             services.AddSingleton<IFeedbackReceiversService, FeedbackReceiversService>();
             services.AddSingleton<ITokensService, TokensService>();
+            services.AddSingleton<IFeedbacksService, FeedbacksService>();
             services.AddSingleton<IMongoClient, MongoClient>(i =>
             {
                 var settings = i.GetService<IOptions<DatabaseSettings>>();
diff --git a/Retroactiune.WebAPI/appsettings.Testing.json b/Retroactiune.WebAPI/appsettings.Testing.json
index ddce3c1..a9d7170 100644
--- a/Retroactiune.WebAPI/appsettings.Testing.json
+++ b/Retroactiune.WebAPI/appsettings.Testing.json
@@ -1,8 +1,8 @@
 {
   "DatabaseSettings": {
-    "FeedbackCollectionName": "feedback",
+    "FeedbackCollectionName": "feedbacks",
     "TokensCollectionName": "tokens",
-    "FeedbackReceiverCollectionName": "feedback_receiver",
+    "FeedbackReceiverCollectionName": "feedback_receivers",
     "ConnectionString": "mongodb://localhost:27017",
     "DatabaseName": "RetroactiuneTesting"
   }
diff --git a/Retroactiune.WebAPI/appsettings.json b/Retroactiune.WebAPI/appsettings.json
index 115992e..7415215 100644
--- a/Retroactiune.WebAPI/appsettings.json
+++ b/Retroactiune.WebAPI/appsettings.json
@@ -1,8 +1,8 @@
 {
   "DatabaseSettings": {
-    "FeedbackCollectionName": "feedback",
+    "FeedbackCollectionName": "feedbacks",
     "TokensCollectionName": "tokens",
-    "FeedbackReceiverCollectionName": "feedback_receiver",
+    "FeedbackReceiverCollectionName": "feedback_receivers",
     "ConnectionString": "mongodb://localhost:27017",
     "DatabaseName": "Retroactiune"
   },