Thanks for sharing these details, and sorry this is still an issue—I’m sure this is frustrating. A couple more things I’d like to ask you to try: can you please regenerate the publishable URL for your app and reinstall using the new URL?:
Next, can you try replacing your endpoints (temporarily) with an endpoint from something like https://requestbin.com/ or similar? I’d like to rule out that there isn’t something we’re not catching with your existing endpoint.
If you update the endpoint for testing, please reinstall the app once more before starting a test meeting.
If none of these do the trick, let me know—I’m happy to private message you and set up some time to troubleshoot this over a Zoom call.