Filers will encounter the "Error 421: Invalid Mexico Postal Code" error when they have provided an incorrect postal (zip) code in the Party Information.
Users will need to edit the Party Information and provide the correct postal code, or remove the address entirely as the first / last name are the only required fields.
Other available countries produce an "Invalid Postal Code" error if the zip code not correct and do not allow the user to proceed beyond the Party Information screen.