iOS/iPadOS fails to authenticate gmail account

Following password updates and setting 2 factor authentication in my gmail accounts on my ipads (iOS 12.4.9 (Air) and iPadOS 14.2 (Pro 11") I get the message "Email Address Mismatch The email address you entered does not match your account". I have followed the advice in a previous post and run https://accounts.google.com/DisplayUnlockCaptcha but it fails to work (I'm not sure ir first asks me which account I'm using - I just get a standard user name request, followed by password and the 2 step authentication code entry) and I just get a repeat of the mismatch message. I have tried deleting the account from my iPadOS 14.2 system and reinstalling it, but I get the same problem and can't reinstall the account. I have tried an app password, but that doesn't work either. However, thunderbird on my PC has worked as has my iphone 7 running iOS 14.2... but they were set up first. My MACbook running 10.15.7 also works. So neither ipad can access my main gmail account at the moment( - disaster)... any ideas