Set CVV as a Required Field with PMPro

my_require_cvv_for_reals.php

<?php

/**
 * Set CVV as a Required Field with PMPro
 * Add this code to a custom plugin. https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 *
 * NOTE: Doesn't yet work with Stripe, Braintree, or PayPal Express (most gateways) that don't pass the CVV to the server.
 */
function my_require_cvv_for_reals( $fields ) {
	if ( ! empty( $_REQUEST['CVV'] ) ) {
		$CVV = sanitize_text_field( $_REQUEST['CVV'] );    
	} elseif ( ! empty( $_REQUEST['StripeToken0'] ) ) {
		$CVV = true;
	} else {
		$CVV = '';
	}
	
	$fields['CVV'] = $CVV;
	
	return $fields;
}
add_filter( 'pmpro_required_billing_fields', 'my_require_cvv_for_reals', 15 );