[Refer A Friend] Custom validation for referral coupons - Restrict coupon use to advocates with active subscriptions

functions.php

<?php


add_filter( 'automatewoo/referrals/validate_coupon_for_user', 'my_automatewoo_referral_coupon_validate', 10, 3 );
add_filter( 'automatewoo/referrals/validate_coupon_for_guest', 'my_automatewoo_referral_coupon_validate', 10, 3 );

/**
 * $valid is true if coupon is valid for user or an instance of WP_Error if the coupon is invalid
 *
 * @param WP_Error|true $valid
 * @param int|string $customer
 * @param int $advocate_id
 * @return WP_Error|true
 */
function my_automatewoo_referral_coupon_validate( $valid, $customer, $advocate_id ) {

	if ( is_wp_error( $valid ) ) {
		// coupon is already invalid so return the validation error
		return $valid;
	}

	/** @var WC_Subscription[] $subscriptions */
	$subscriptions = wcs_get_users_subscriptions( $advocate_id );
	$statuses = [];

	foreach ( $subscriptions as $subscription ) {
		$statuses[] = $subscription->get_status();
	}

	if ( count( array_intersect( $statuses, [ 'active', 'pending-cancel' ] ) ) === 0 ) {
		return new WP_Error( 'coupon-invalid', __( 'This coupon is invalid.', 'my-theme' ) );
	}

	return true; // allow coupon use
}