bh-wc-check-coupon-allowed-emails-earlier.php

<?php
/**
 * @wordpress-plugin
 * Plugin Name:       Check Coupon Allowed Emails Earlier
 * Description:       Compares the billing email address to coupons' "Allowed Emails" restrictions anytime the checkout is updated.
 * Plugin URI:        https://github.com/woocommerce/woocommerce/issues/28560
 * Version:           1.0.0
 * Author:            BrianHenryIE
 * License:           GPL-2.0+
 * License URI:       http://www.gnu.org/licenses/gpl-2.0.txt
 * Text Domain:       bh-wc-check-coupon-allowed-emails-earlier
 * Domain Path:       /languages
 */


/**
 * @see WC_AJAX::update_order_review()
 *
 * @param string $posted_data_string Unparsed, unslashed posted data.
 */
add_action( 'woocommerce_checkout_update_order_review', function ( string $posted_data_string ) {

	if( 1 !== preg_match('/billing_email=([^&]*)/', $posted_data_string, $output_array) ) {
		return;
	}

	$billing_email = urldecode($output_array[1]);

	if( ! is_email( $billing_email ) ) {
		return;
	}

	$coupon_codes = WC()->cart->get_applied_coupons();

	foreach( $coupon_codes as $coupon_code ) {

		$coupon_id = wc_get_coupon_id_by_code( $coupon_code );

		if( 0 === $coupon_id ) {
			continue;
		}

		$coupon = new WC_Coupon( $coupon_id );

		$email_restrictions = $coupon->get_email_restrictions();

		if( empty( $email_restrictions ) ){
			continue;
		}

		if( ! in_array( $billing_email, $coupon->get_email_restrictions(), true ) ) {

			WC()->cart->remove_coupon( $coupon_code );
			wc_add_notice("Coupon \"<em>$coupon_code</em>\" not valid for this email address", 'error' );
		}
	}

});