What to do when Gmail account already added but not activated on iPad

On my iPad I had Gmail, I then also got Email. When I went onto Email I was trying to use a different account to sign in using Google. Once I had signed in it came up with a notification saying:

”Gmail” is already added

This Gmail account has already been added to your iPad but is not activated. Please activate the account in Settings.

So I went to settings and checked and it was already activated. I tried deactivating it and then activating it agin but it still doesn’t work.

What do I do?

[Re-Titled by Moderator]