diff --git a/src/Digdir.Domain.Dialogporten.Application/Features/V1/ServiceOwner/Dialogs/Commands/Create/CreateDialogCommand.cs b/src/Digdir.Domain.Dialogporten.Application/Features/V1/ServiceOwner/Dialogs/Commands/Create/CreateDialogCommand.cs
index 4ccb7fd14..ee4edf988 100644
--- a/src/Digdir.Domain.Dialogporten.Application/Features/V1/ServiceOwner/Dialogs/Commands/Create/CreateDialogCommand.cs
+++ b/src/Digdir.Domain.Dialogporten.Application/Features/V1/ServiceOwner/Dialogs/Commands/Create/CreateDialogCommand.cs
@@ -7,6 +7,7 @@
 using Digdir.Domain.Dialogporten.Domain.Dialogs.Entities;
 using Digdir.Domain.Dialogporten.Domain.Dialogs.Entities.Activities;
 using Digdir.Domain.Dialogporten.Domain.Dialogs.Entities.Attachments;
+using Digdir.Domain.Dialogporten.Domain.Dialogs.Entities.Transmissions;
 using FluentValidation.Results;
 using MediatR;
 using OneOf;
@@ -121,6 +122,12 @@ public async Task<CreateDialogResult> Handle(CreateDialogCommand request, Cancel
             _domainContext.AddError(DomainFailure.EntityExists<DialogAttachment>(existingAttachmentIds));
         }
 
+        var existingTransmissionIds = await _db.GetExistingIds(dialog.Transmissions, cancellationToken);
+        if (existingTransmissionIds.Count != 0)
+        {
+            _domainContext.AddError(DomainFailure.EntityExists<DialogTransmission>(existingTransmissionIds));
+        }
+
         await _db.Dialogs.AddAsync(dialog, cancellationToken);
 
         var saveResult = await _unitOfWork.SaveChangesAsync(cancellationToken);
diff --git a/src/Digdir.Domain.Dialogporten.Application/Features/V1/ServiceOwner/Dialogs/Commands/Update/UpdateDialogCommand.cs b/src/Digdir.Domain.Dialogporten.Application/Features/V1/ServiceOwner/Dialogs/Commands/Update/UpdateDialogCommand.cs
index 9f8764a33..f9d8020a9 100644
--- a/src/Digdir.Domain.Dialogporten.Application/Features/V1/ServiceOwner/Dialogs/Commands/Update/UpdateDialogCommand.cs
+++ b/src/Digdir.Domain.Dialogporten.Application/Features/V1/ServiceOwner/Dialogs/Commands/Update/UpdateDialogCommand.cs
@@ -110,13 +110,14 @@ public async Task<UpdateDialogResult> Handle(UpdateDialogCommand request, Cancel
         _mapper.Map(request.Dto, dialog);
         ValidateTimeFields(dialog);
 
-        AppendActivity(dialog, request.Dto);
+        await AppendActivity(dialog, request.Dto, cancellationToken);
         VerifyActivityRelations(dialog);
 
-        AppendTransmission(dialog, request.Dto);
-        VerifyActivityTransmissionRelations(dialog);
+        await AppendTransmission(dialog, request.Dto, cancellationToken);
         VerifyTransmissionRelations(dialog);
 
+        VerifyActivityTransmissionRelations(dialog);
+
         dialog.SearchTags
             .Merge(request.Dto.SearchTags,
                 destinationKeySelector: x => x.Value,
@@ -205,19 +206,16 @@ private void ValidateTimeFields(DialogEntity dialog)
         }
     }
 
-    private void AppendActivity(DialogEntity dialog, UpdateDialogDto dto)
+    private async Task AppendActivity(DialogEntity dialog, UpdateDialogDto dto, CancellationToken cancellationToken)
     {
         var newDialogActivities = _mapper.Map<List<DialogActivity>>(dto.Activities);
 
-        var existingIds = dialog.Activities.Select(x => x.Id).ToList();
-
-        existingIds = existingIds.Intersect(newDialogActivities.Select(x => x.Id)).ToList();
+        var existingIds = await _db.GetExistingIds(newDialogActivities, cancellationToken);
         if (existingIds.Count != 0)
         {
             _domainContext.AddError(
                 nameof(UpdateDialogDto.Activities),
                 $"Entity '{nameof(DialogActivity)}' with the following key(s) already exists: ({string.Join(", ", existingIds)}).");
-            return;
         }
 
         dialog.Activities.AddRange(newDialogActivities);
@@ -280,19 +278,16 @@ private void VerifyActivityRelations(DialogEntity dialog)
         }
     }
 
-    private void AppendTransmission(DialogEntity dialog, UpdateDialogDto dto)
+    private async Task AppendTransmission(DialogEntity dialog, UpdateDialogDto dto, CancellationToken cancellationToken)
     {
         var newDialogTransmissions = _mapper.Map<List<DialogTransmission>>(dto.Transmissions);
 
-        var existingIds = dialog.Transmissions.Select(x => x.Id).ToList();
-
-        existingIds = existingIds.Intersect(newDialogTransmissions.Select(x => x.Id)).ToList();
+        var existingIds = await _db.GetExistingIds(newDialogTransmissions, cancellationToken);
         if (existingIds.Count != 0)
         {
             _domainContext.AddError(
                 nameof(UpdateDialogDto.Transmissions),
                 $"Entity '{nameof(DialogTransmission)}' with the following key(s) already exists: ({string.Join(", ", existingIds)}).");
-            return;
         }
 
         dialog.Transmissions.AddRange(newDialogTransmissions);
@@ -303,7 +298,11 @@ private void AppendTransmission(DialogEntity dialog, UpdateDialogDto dto)
 
     private void VerifyTransmissionRelations(DialogEntity dialog)
     {
-        var relatedTransmissionIds = dialog.Transmissions.Where(x => x.RelatedTransmissionId is not null).Select(x => x.RelatedTransmissionId).ToList();
+        var relatedTransmissionIds = dialog.Transmissions
+            .Where(x => x.RelatedTransmissionId is not null)
+            .Select(x => x.RelatedTransmissionId)
+            .ToList();
+
         if (relatedTransmissionIds.Count == 0)
         {
             return;