Might be temporary Apple outage. See:
https://developer.apple.com/forums/thread/705599
Here’s a workaround:
-
Organizer -> Distribute App -> App Store Connect -> Export -> NOW DISABLE WIFI / INTERNET (else will fail) -> Exported .ipa
-
Now use Transporter App -> Login to same account -> Add .ipa -> Upload works !
Transporter can be downloaded here:
https://apps.apple.com/app/transporter/id1450874784