1. Account type
Work/school and personal Microsoft accounts use different entry points. Check your invite email.
2. Network
Switch from public Wi‑Fi to mobile data and retry.
3. Device clock
Enable automatic date & time.
4. Clear cache / reinstall
Clear app cache, then reinstall the APK if needed.
5. Org policy
Conditional access may block unmanaged devices—share the exact error with your admin.
For a quick meeting, try the web app.