I"m sorry to hear this issue is still troubling you! To be transparent with you, the 500 error is almost always related to the query that is sent - if it isn’t formatted correctly, the platform will block the API request and send back a 500 error, as it can’t process the data normally. Does that make sense?
I do agree this is something that we could improve on, and I’ll pass that as feedback to our development team That said, I do think @JCorrell has a very good point here and after adding a comma, the mutation should work correctly.