After trying to go through the TestFlight upload, I got an error message after pressing Save and Continue saying:
"We weren’t able to verify your App Store Connect Credentials.
Invalid username and password combination. Used ***@gmail.com’ as the username."
I have retyped the Apple ID password and email in many times and it is definitely correct. I was wondering if anyone knew why the error is happening and what to do about it?
I had such error several times. It either disappeared by itself in a few hours, or there was an issue with Apple Developer account on the Apple side.
You may want to contact Adalo support here Right Desk, they may have more info in the logs.