AA9/12 Error: PREFISSO TELEFONICO ERRATO

This error can appear even when the phone number looks correct in international format.

Wrong Format

Prefisso: +39
Telefono: 3514059337

Corrected Format

Prefisso: 351
Telefono: 4059337

Do not use +39, spaces or special symbols in this field. For an Italian mobile number, split the mobile prefix from the remaining digits.

Lesson

Official wording can be ambiguous. When the software says the prefix is wrong, it may be asking for the mobile operator prefix, not the international country prefix.