Appstore won’t accept phone number when changing country/region

Hi,

I’m trying to change my Apple ID region to Italy and the format in the Phone field is: 123 | 123456789.

My number has 10 numbers (not 9 like the second part in the field) and I’ve tried many variations, including with the country code (39 and 039) in the first part of the field.

How do I have to format my phone number?

Thank you.