Can't Log In in Facebook

hello

a friend bought an iphone 6s from us.

and his account on facebook got banned for sending a sexual material on massenger to another friend,

so when he created another facebook account and try to login from his iphone , It says "Login Failed" Sorry, an unexpected error occurred. Please try again later."

he tried to log in with many facebook accounts of his friends but he gets the same massage.

he can log in to facebook if he does it through the browser on his iphone and he can log in from any other device (andriod mobile or pc)

he deleted the app and reinstall it again

he tried to make factory reset and reset network settings

and he tried to login with another icloud account (a friend's account)

but he gets everytime the same massage

so what should he do please?

making new software to the device?

[Re-Titled by Moderator]