I have a problem with a new created attachments detail in a tab.
I have created a new "Event" tab and I have added "Attachments" detail. Also, I have changed the parent for Schema16Detail object to "FileDetailV2 ( UIv2 )".
When I'm trying to upload a file in attachments, I receive the following error:
The entity for the attachments must be named "ParentEntityFile", so in your case that looks like OtpEventFile, and must also have "File" object as it's parent (not base object). Then you'd add a lookup to relate it to the parent OtpEvent.