Hi Tom,
Yes, you cannot directly add it to the viewset BP_DATA/AccountContactViewset since it has already been added in the window BP_DATA/MarketingAttributesEOVPList once. That is why I had mentioned above to create a component usage and then add the same.
You can create a component usage for the InterfaceView BP_DATA/MarketingAttributesEOVPList and add it to the viewset BP_DATA/AccountContactViewset.
Thanks & Best Regards,
Leon