Make sure address fields are required

my_pmpro_required_billing_fields.php

<?php
/**
 * Make sure address fields are required
 */
function my_pmpro_required_billing_fields( $fields ) {
    global $bfirstname, $blastname, $baddress1, $bcity, $bstate, $bzipcode, $bcountry, $bphone, $bemail;
    $fields[ 'bfirstname' ] = $bfirstname;
    $fields[ 'blastname' ] = $blastname;
    $fields[ 'baddress1' ] = $baddress1;
    $fields[ 'bcity' ] = $bcity;
    $fields[ 'bzipcode' ] = $bzipcode;
    $fields[ 'bemail' ] = $bemail;
    return $fields;
}
add_action( 'pmpro_required_billing_fields', 'my_pmpro_required_billing_fields', 30 );