After trying to log a client into my Meta App (using Facebook Login for Business), I found that their account is marked as restricted and it is failing to log in. There is a message saying "Turn on two-factor authentication to gain access to your business accounts and assets"
After clicking 'Secure Your Account' it takes me to a page saying that two-factor authentication is already set up:
I also tried accessing it from their 'personal' Facebook profile, but it says it is already turned on there too:
Are there more settings somewhere that can be used to fix this and remove the account restrictions?
Turning the 2FA off and then on again solved it for me.