Change country/region

My son just came to the US from Mexico and brought his iphone 14 pro with him, but we’re trying to change the country/region so he can download some app and its not letting him do it.

He doesn’t subcriptions of any kind.

Everytime we try to change we get a screen that says he needs to finish his money from the appleID

How can we tid this?

Thank you for your help in advance.