Had a similar experience when integrating with Microsoft Teams. The integration worked OK for 99% users, but for 1% users we were getting some vague "not supported" errors without explaining anything (what's wrong or how to fix it), sometimes just 500's. Nothing in the documentation about the errors. Filed a ticket, the support guy gave a few suggestions, but it was clear he didn't really understand the documentation himself, I explained why his reading of the documentation was demonstrably wrong and had nothing to do with my problem, he agreed and promised to escalate to the actual dev team. Haven't heard from them since then (it was several months ago). I've had several such interactions with MS which led to nowhere. Meanwhile a competitor (we integrated with, too) used to solve all our problems in 1-3 work days.