Hi Marco,

The plugin doesn't have this functionality by default. VAT is a special field, there's no way to create other fields like it.

But if you want, I can give you some JS code to add to functions.php that would set this up.

This field should be REQUIRED and VISIBLE for ITALY and INVISIBLE for all other countries, correct?

If you can give me a link to your registration page with this field, it would be even better, I could test directly in the site.

This code should work if you replace fieldInput and fieldContainer with the html input and its container in the form:

var fieldContainer = jQuery('input[name="b2bking_custom_field_263"]').parent().parent();
var fieldInput = jQuery('input[name="b2bking_custom_field_263"]');
showHideRegistrationFieldsItaly();
jQuery('.b2bking_country_field_selector select').change(showHideRegistrationFieldsItaly);
jQuery('select#billing_country').change(showHideRegistrationFieldsItaly);
jQuery('select#b2bking_registration_roles_dropdown').change(showHideRegistrationFieldsItaly);
function showHideRegistrationFieldsItaly(){
    let selectedRole = jQuery('#b2bking_registration_roles_dropdown').val();
    let roleDisplay = jQuery('#b2bking_registration_roles_dropdown').css('display');
    let hiddenRole = false;
    if (roleDisplay !== 'inline-block' && roleDisplay !== 'block'){
        hiddenRole = true;
    }
    if (hiddenRole === true || fieldContainer.hasClass('b2bking_custom_registration_'+selectedRole) || fieldContainer.hasClass('b2bking_custom_registration_allroles')){
        let selectedCountry = jQuery('.b2bking_country_field_selector select').val();
        if (selectedCountry === undefined){
            selectedCountry = jQuery('select#billing_country').val();
        }
        if (selectedCountry === 'IT'){
            // required and visible
            fieldInput.prop('required', true);
            fieldContainer.css('display', 'block');
        } else {
            // not required and hidden
            fieldInput.removeAttr('required');
            fieldContainer.css('display', 'none');
        }
    } else {
        // not required and hidden
        fieldInput.removeAttr('required');
        fieldContainer.css('display', 'none');
    }
}

Or if you can share a link to you registration page and which field it is, I can make the code more precise to your site.