Apparently DICE does not allow including a UNION type parameter in the _construct of the class because on line 257 of the code it tries to create a checking function ('is...) and the returned string ...

c_ws_plugin__s2member_pro_coupons::log_user_coupons_use() in /var/www/clients/client0/web4/web/wp-content/plugins/s2member/src/includes/classes/paypal-notify-in-wa ...