Hi @KirstenMickow @willpklein,
Looking at the log file the error is:
"code": 400,
"details": [
"This operation is not supported."
],
"message": ""
It sounds as though there is an issue with the feature service and possible sharing permissions or capabilities. Are you using a WHERE clause for filtering the Inbox?
It would probably be best to raise this with Esri Support, so an analyst can work with you directly and gather more information (logs, configurations, settings etc) to diagnose the problem further.
Regards,
Phil.