I suspect what's going on is that TikTok is trying to access user data on the phone that, after the latest Apple update, requires the user to authorized that access, by entering the phone password.
And so entering a phony password will not work; access won't be granted, it will prompt again until either the real password is entered, or the user Cancels out.
And that's how you tell what's up - THEIR software can't tell the password is phony until it tries to sign in to get access to the IPhone and its data.