gmail on iphone mail app - "cannot get mail - gmail is currently unavailable" - help!

I'm trying to add my daughter's gmail account to the mail app on her iphone 8. But after adding everything and authorising it, I just get the "cannot get mail - gmail is currently unavailable" error message.

I've tried uninstalling the mail app, deleteing and adding her gmail details, and even resetting the network settings.. I even tried turning it off and on again -- but just get the same error.

I've then tried searching for similar issues online but found nothing. I'm convinced it must be some box that isn't ticked or related to the google family security stuff, but I can't figure out what I need to do to resolve it.

Have any community members had similar issues? Can you advise how to fix it?

Thanks!