Reward friend during registration

functions.php

<?php

add_action('user_register', 'wpgens_generate_referral_reward', 10, 1);

function wpgens_generate_referral_reward($user_id)
{
	if (isset($_COOKIE["gens_raf"])) {
		global $wpdb;
		$results = $wpdb->get_results($wpdb->prepare("SELECT user_id FROM $wpdb->usermeta WHERE meta_key='gens_referral_id' AND meta_value = %s", sanitize_text_field($_COOKIE["gens_raf"])));
		if (!empty($results)) {
			$referral_id = (int)$results[0]->user_id;
		}
		if (!$referral_id && filter_var($_COOKIE["gens_raf"], FILTER_VALIDATE_EMAIL)) {
			$referral_id = sanitize_text_field($_COOKIE["gens_raf"]);
		}
		if (!$referral_id) {
			return;
		}

		do_action('gens_new_user_registration', $referral_id, $user_id);

		do_action('new_raf_data', 'user_referred', array('user' => $user_id, 'referrer' => $referral_id));

		$friend_coupon_object = new WPGens_RAF_Coupons('registration', $user_id, 0);

		$friend_coupon_code   = $friend_coupon_object->get_coupon();
		$email = new WPGens_RAF_Email($friend_coupon_object->coupon_mail, $friend_coupon_code, 0, 'friend');
		$email->send_email();
	}
}