user registration reward

functions.php

<?php

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

function generate_coupon( $user_id ) {
  if(isset($_COOKIE["gens_raf"])) {
      $referral_code = $_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", $referral_code));
      if(!empty($results)) {
          $user_id = (int)$results[0]->user_id;
      } 
      // You got ID of user that referred friend, now create a coupon and assign it to him. Check WPGens_RAF_Coupons class.
  }
  
}


?>