diff --git a/CallbackHander.Testing/TestData.cs b/CallbackHander.Testing/TestData.cs
index 6212a21..3e670b5 100644
--- a/CallbackHander.Testing/TestData.cs
+++ b/CallbackHander.Testing/TestData.cs
@@ -31,6 +31,22 @@ public class TestData
             TestData.TypeString,
             TestData.Reference);
 
+    public static CallbackCommands.RecordCallbackCommand RecordCallbackCommandEmptyReference =>
+        new(TestData.CallbackId,
+            TestData.CallbackMessage,
+            TestData.Destinations,
+            (MessageFormat)TestData.MessageFormat,
+            TestData.TypeString,
+            String.Empty);
+
+    public static CallbackCommands.RecordCallbackCommand RecordCallbackCommandInvalidReference =>
+        new(TestData.CallbackId,
+            TestData.CallbackMessage,
+            TestData.Destinations,
+            (MessageFormat)TestData.MessageFormat,
+            TestData.TypeString,
+            "reference");
+
     public static CallbackQueries.GetCallbackQuery GetCallbackQuery =>
         new CallbackQueries.GetCallbackQuery(TestData.CallbackId);
 
diff --git a/CallbackHandler.BusinessLogic.Tests/Services/CallbackDomainServiceTests.cs b/CallbackHandler.BusinessLogic.Tests/Services/CallbackDomainServiceTests.cs
index 0b84fad..82b6052 100644
--- a/CallbackHandler.BusinessLogic.Tests/Services/CallbackDomainServiceTests.cs
+++ b/CallbackHandler.BusinessLogic.Tests/Services/CallbackDomainServiceTests.cs
@@ -3,6 +3,7 @@
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
+using SimpleResults;
 
 namespace CallbackHandler.BusinessLogic.Tests.Services;
 
@@ -25,15 +26,27 @@ public class CallbackDomainServiceTests
     public CallbackDomainServiceTests() {
         this.AggregateRepository = new Mock<IAggregateRepository<CallbackMessageAggregate, DomainEvent>>();
         this.DomainService = new CallbackDomainService(this.AggregateRepository.Object);
-        
+        this.AggregateRepository.Setup(a => a.GetLatestVersion(It.IsAny<Guid>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync(TestData.EmptyCallbackMessageAggregate());
+        this.AggregateRepository.Setup(a => a.SaveChanges(It.IsAny<CallbackMessageAggregate>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync(Result.Success);
     }
 
     [Fact]
     public async Task CallbackDomainService_RecordCallback_CallbackRecorded() {
-        this.AggregateRepository.Setup(a => a.GetLatestVersion(It.IsAny<Guid>(), It.IsAny<CancellationToken>()))
-                               .ReturnsAsync(TestData.EmptyCallbackMessageAggregate());
+        Result result = await this.DomainService.RecordCallback(TestData.RecordCallbackCommand, CancellationToken.None);
+        result.IsSuccess.ShouldBeTrue();
+    }
 
-        Should.NotThrow(async () => await this.DomainService.RecordCallback(TestData.RecordCallbackCommand,
-                                                                            CancellationToken.None));
+    [Fact]
+    public async Task CallbackDomainService_RecordCallback_EmptyReference_ResultFailed() {
+        Result result = await this.DomainService.RecordCallback(TestData.RecordCallbackCommandEmptyReference, CancellationToken.None);
+        result.IsFailed.ShouldBeTrue();
+    }
+
+    [Fact]
+    public async Task CallbackDomainService_RecordCallback_InvalidReference_ResultFailed() {
+        Result result = await this.DomainService.RecordCallback(TestData.RecordCallbackCommandInvalidReference, CancellationToken.None);
+        result.IsFailed.ShouldBeTrue();
     }
 }
diff --git a/CallbackHandler.BusinessLogic/Services/CallbackDomainService.cs b/CallbackHandler.BusinessLogic/Services/CallbackDomainService.cs
index b4084b7..c3881d2 100644
--- a/CallbackHandler.BusinessLogic/Services/CallbackDomainService.cs
+++ b/CallbackHandler.BusinessLogic/Services/CallbackDomainService.cs
@@ -3,7 +3,7 @@
 
 namespace CallbackHandler.BusinessLogic.Services;
 
-using CallbackHandler.BusinessLogic.Requests;
+using Requests;
 using CallbackMessageAggregate;
 using Shared.DomainDrivenDesign.EventSourcing;
 using Shared.EventStore.Aggregate;
@@ -11,6 +11,12 @@ namespace CallbackHandler.BusinessLogic.Services;
 using System.Threading;
 using System.Threading.Tasks;
 
+public interface ICallbackDomainService
+{
+    Task<Result> RecordCallback(CallbackCommands.RecordCallbackCommand command,
+                                CancellationToken cancellationToken);
+}
+
 public class CallbackDomainService : ICallbackDomainService
 {
     private readonly IAggregateRepository<CallbackMessageAggregate, DomainEvent> AggregateRepository;
@@ -23,12 +29,16 @@ public async Task<Result> RecordCallback(CallbackCommands.RecordCallbackCommand
                                              CancellationToken cancellationToken) {
 
         // split the reference string into an array of strings
-        String[] referenceData = command.Reference?.Split(new[] { '-' }, StringSplitOptions.RemoveEmptyEntries) ?? Array.Empty<string>();
-        // TODO: Validate the reference data has the correct number of elements
+        String[] referenceData = command.Reference?.Split(['-'], StringSplitOptions.RemoveEmptyEntries) ?? [];
+
         if (referenceData.Length == 0) {
             return Result.Invalid("Reference cannot be empty.");
         }
 
+        if (referenceData.Length != 2) {
+            return Result.Invalid("Reference must contain estate and merchant references separated by a hyphen.");
+        }
+
         // Element 0 is estate reference, Element 1 is merchant reference
         String estateReference = referenceData[0];
         String merchantReference = referenceData[1];
diff --git a/CallbackHandler.BusinessLogic/Services/ICallbackDomainService.cs b/CallbackHandler.BusinessLogic/Services/ICallbackDomainService.cs
deleted file mode 100644
index a12b88b..0000000
--- a/CallbackHandler.BusinessLogic/Services/ICallbackDomainService.cs
+++ /dev/null
@@ -1,19 +0,0 @@
-using Azure.Core;
-using CallbackHandlers.Models;
-using MediatR;
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading;
-using System.Threading.Tasks;
-using CallbackHandler.BusinessLogic.Requests;
-using SimpleResults;
-
-namespace CallbackHandler.BusinessLogic.Services;
-
-public interface ICallbackDomainService
-{
-    Task<Result> RecordCallback(CallbackCommands.RecordCallbackCommand command,
-                                CancellationToken cancellationToken);
-}