Changed to abstract type
diff --git a/sdks/dotnet/basyx-core/BaSyx.API/Components/ServiceProvider/SubmodelServiceProvider.cs b/sdks/dotnet/basyx-core/BaSyx.API/Components/ServiceProvider/SubmodelServiceProvider.cs
index 351fde5..51894c5 100644
--- a/sdks/dotnet/basyx-core/BaSyx.API/Components/ServiceProvider/SubmodelServiceProvider.cs
+++ b/sdks/dotnet/basyx-core/BaSyx.API/Components/ServiceProvider/SubmodelServiceProvider.cs
@@ -288,7 +288,7 @@
             return new Result<InvocationResponse>(operation_Retrieved);
         }
 
-        private OperationVariableSet CreateOutputArguments(OperationVariableSet outputVariables)
+        private IOperationVariableSet CreateOutputArguments(IOperationVariableSet outputVariables)
         {
             if (outputVariables == null)
                 return null;