Integration with ipay88

Hi Sir
I do try to install your Sequential Order Number for WooCommerce into my system , but it seem like not compatible with ipay88 payment gateway. It will getting error as below :

Fatal error: Uncaught Error: Call to a member function get_total() on bool in /home/domain/public_html/wp-content/plugins/woocommerce-gateway-ipay88/includes/class-wc-gateway-ipay88.php:540 Stack trace: #0 /home/domain/public_html/wp-content/plugins/woocommerce-gateway-ipay88/includes/class-wc-gateway-ipay88.php(579): WC_Gateway_iPay88->validate_response() #1 /home/domain/public_html/wp-includes/class-wp-hook.php(303): WC_Gateway_iPay88->check_status_response_ipay88('') #2 /home/domain/public_html/wp-includes/class-wp-hook.php(327): WP_Hook->apply_filters('', Array) #3 /home/domain/public_html/wp-includes/plugin.php(470): WP_Hook->do_action(Array) #4 /home/domain/public_html/wp-content/plugins/woocommerce/includes/class-wc-api.php(161): do_action('woocommerce_api...') #5 /home/domain/public_html/wp-includes/class-wp-hook.php(303): WC_API->handle_api_requests(Object(WP)) #6 /home/domain/public_html/wp-includes/class-wp-hook.php(327): WP_Hook->a in /home/saikee/public_html/wp-content/plugins/woocommerce-gateway-ipay88/includes/class-wc-gateway-ipay88.php on line 540

I do found another user also facing same issues & he manage to solve it “Integration with Payment Plugin (iPay88)”

May i know where he add for “private function get_order_id( $order_number ) {” ?

Kindly advice , thanks