Hi
I am posting this in case someone in the future ends up here.
I faced the same issue. In the Chrome console, I could see 503 errors (service unavailable).
I tried most solutions posted online (appending verification code, using another device, logging to to iCloud then App Connect) but all failed for me.
After around 5 hours, I tried again, but this time it was on a different network (same device and browser). And it let me sign in ( however, it asked for a verification code from my iOS device).
Topic:
App Store Distribution & Marketing
SubTopic:
App Store Connect
Tags: