diff --git a/src/Api/Auth/Controllers/AuthRequestsController.cs b/src/Api/Auth/Controllers/AuthRequestsController.cs
index c62b817905..e4a9027f20 100644
--- a/src/Api/Auth/Controllers/AuthRequestsController.cs
+++ b/src/Api/Auth/Controllers/AuthRequestsController.cs
@@ -102,7 +102,37 @@ public class AuthRequestsController(
     public async Task<AuthRequestResponseModel> Put(Guid id, [FromBody] AuthRequestUpdateRequestModel model)
     {
         var userId = _userService.GetProperUserId(User).Value;
+
+        // If the Approving Device is attempting to approve a request, validate the approval
+        if (model.RequestApproved == true)
+        {
+            await ValidateApprovalOfMostRecentAuthRequest(id, userId);
+        }
+
         var authRequest = await _authRequestService.UpdateAuthRequestAsync(id, userId, model);
         return new AuthRequestResponseModel(authRequest, _globalSettings.BaseServiceUri.Vault);
     }
+
+    private async Task ValidateApprovalOfMostRecentAuthRequest(Guid id, Guid userId)
+    {
+        // Get the current auth request to find the device identifier
+        var currentAuthRequest = await _authRequestService.GetAuthRequestAsync(id, userId);
+        if (currentAuthRequest == null)
+        {
+            throw new NotFoundException();
+        }
+
+        // Get all pending auth requests for this user (returns most recent per device)
+        var pendingRequests = await _authRequestRepository.GetManyPendingAuthRequestByUserId(userId);
+
+        // Find the most recent request for the same device
+        var mostRecentForDevice = pendingRequests
+            .FirstOrDefault(pendingRequest => pendingRequest.RequestDeviceIdentifier == currentAuthRequest.RequestDeviceIdentifier);
+
+        var isMostRecentRequestForDevice = mostRecentForDevice?.Id == id;
+        if (!isMostRecentRequestForDevice)
+        {
+            throw new BadRequestException("This request is no longer valid. Make sure to approve the most recent request.");
+        }
+    }
 }
diff --git a/test/Api.Test/Auth/Controllers/AuthRequestsControllerTests.cs b/test/Api.Test/Auth/Controllers/AuthRequestsControllerTests.cs
index 1b8e7aba8e..fc7eb0d93b 100644
--- a/test/Api.Test/Auth/Controllers/AuthRequestsControllerTests.cs
+++ b/test/Api.Test/Auth/Controllers/AuthRequestsControllerTests.cs
@@ -222,7 +222,7 @@ public class AuthRequestsControllerTests
     }
 
     [Theory, BitAutoData]
-    public async Task Put_ReturnsAuthRequest(
+    public async Task Put_WithRequestNotApproved_ReturnsAuthRequest(
         SutProvider<AuthRequestsController> sutProvider,
         User user,
         AuthRequestUpdateRequestModel requestModel,
@@ -230,6 +230,7 @@ public class AuthRequestsControllerTests
     {
         // Arrange
         SetBaseServiceUri(sutProvider);
+        requestModel.RequestApproved = false; // Not an approval, so validation should be skipped
 
         sutProvider.GetDependency<IUserService>()
             .GetProperUserId(Arg.Any<ClaimsPrincipal>())
@@ -248,6 +249,117 @@ public class AuthRequestsControllerTests
         Assert.IsType<AuthRequestResponseModel>(result);
     }
 
+    [Theory, BitAutoData]
+    public async Task Put_WithApprovedRequest_ValidatesAndReturnsAuthRequest(
+        SutProvider<AuthRequestsController> sutProvider,
+        User user,
+        AuthRequestUpdateRequestModel requestModel,
+        AuthRequest currentAuthRequest,
+        AuthRequest updatedAuthRequest,
+        List<PendingAuthRequestDetails> pendingRequests)
+    {
+        // Arrange
+        SetBaseServiceUri(sutProvider);
+        requestModel.RequestApproved = true; // Approval triggers validation
+        currentAuthRequest.RequestDeviceIdentifier = "device-identifier-123";
+
+        // Setup pending requests - make the current request the most recent for its device
+        var mostRecentForDevice = new PendingAuthRequestDetails(currentAuthRequest, Guid.NewGuid());
+        pendingRequests.Add(mostRecentForDevice);
+
+        sutProvider.GetDependency<IUserService>()
+            .GetProperUserId(Arg.Any<ClaimsPrincipal>())
+            .Returns(user.Id);
+
+        // Setup validation dependencies
+        sutProvider.GetDependency<IAuthRequestService>()
+            .GetAuthRequestAsync(currentAuthRequest.Id, user.Id)
+            .Returns(currentAuthRequest);
+
+        sutProvider.GetDependency<IAuthRequestRepository>()
+            .GetManyPendingAuthRequestByUserId(user.Id)
+            .Returns(pendingRequests);
+
+        sutProvider.GetDependency<IAuthRequestService>()
+            .UpdateAuthRequestAsync(currentAuthRequest.Id, user.Id, requestModel)
+            .Returns(updatedAuthRequest);
+
+        // Act
+        var result = await sutProvider.Sut
+                .Put(currentAuthRequest.Id, requestModel);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.IsType<AuthRequestResponseModel>(result);
+    }
+
+    [Theory, BitAutoData]
+    public async Task Put_WithApprovedRequest_CurrentAuthRequestNotFound_ThrowsNotFoundException(
+        SutProvider<AuthRequestsController> sutProvider,
+        User user,
+        AuthRequestUpdateRequestModel requestModel,
+        Guid authRequestId)
+    {
+        // Arrange
+        requestModel.RequestApproved = true; // Approval triggers validation
+
+        sutProvider.GetDependency<IUserService>()
+            .GetProperUserId(Arg.Any<ClaimsPrincipal>())
+            .Returns(user.Id);
+
+        // Current auth request not found
+        sutProvider.GetDependency<IAuthRequestService>()
+            .GetAuthRequestAsync(authRequestId, user.Id)
+            .Returns((AuthRequest)null);
+
+        // Act & Assert
+        var exception = await Assert.ThrowsAsync<NotFoundException>(
+            () => sutProvider.Sut.Put(authRequestId, requestModel));
+    }
+
+    [Theory, BitAutoData]
+    public async Task Put_WithApprovedRequest_NotMostRecentForDevice_ThrowsBadRequestException(
+        SutProvider<AuthRequestsController> sutProvider,
+        User user,
+        AuthRequestUpdateRequestModel requestModel,
+        AuthRequest currentAuthRequest,
+        List<PendingAuthRequestDetails> pendingRequests)
+    {
+        // Arrange
+        requestModel.RequestApproved = true; // Approval triggers validation
+        currentAuthRequest.RequestDeviceIdentifier = "device-identifier-123";
+
+        // Setup pending requests - make a different request the most recent for the same device
+        var differentAuthRequest = new AuthRequest
+        {
+            Id = Guid.NewGuid(), // Different ID than current request
+            RequestDeviceIdentifier = currentAuthRequest.RequestDeviceIdentifier,
+            UserId = user.Id,
+            Type = AuthRequestType.AuthenticateAndUnlock,
+            CreationDate = DateTime.UtcNow
+        };
+        var mostRecentForDevice = new PendingAuthRequestDetails(differentAuthRequest, Guid.NewGuid());
+        pendingRequests.Add(mostRecentForDevice);
+
+        sutProvider.GetDependency<IUserService>()
+            .GetProperUserId(Arg.Any<ClaimsPrincipal>())
+            .Returns(user.Id);
+
+        sutProvider.GetDependency<IAuthRequestService>()
+            .GetAuthRequestAsync(currentAuthRequest.Id, user.Id)
+            .Returns(currentAuthRequest);
+
+        sutProvider.GetDependency<IAuthRequestRepository>()
+            .GetManyPendingAuthRequestByUserId(user.Id)
+            .Returns(pendingRequests);
+
+        // Act & Assert
+        var exception = await Assert.ThrowsAsync<BadRequestException>(
+            () => sutProvider.Sut.Put(currentAuthRequest.Id, requestModel));
+
+        Assert.Equal("This request is no longer valid. Make sure to approve the most recent request.", exception.Message);
+    }
+
     private void SetBaseServiceUri(SutProvider<AuthRequestsController> sutProvider)
     {
         sutProvider.GetDependency<IGlobalSettings>()