version Zencart 1.5.6C PHP 7.3 Using Bootstrap Template
Can someone tell me how to correct this sort of error undefined constant, thanks

Request URI: /ipn_main_handler.php,
--> PHP Warning: Use of undefined constant MODULE_PAYMENT_PAYPALWPP_REFUNDED_STATUS_ID - assumed 'MODULE_PAYMENT_PAYPALWPP_REFUNDED_STATUS_ID' (this will throw an Error in a future version of PHP) in /var/www/vhosts/domain/httpdocs/ipn_main_handler.php on line 446.