Fatal error: Uncaught Error: Call to a member function process_payment() on null in /var/www/html/wp-content/plugins/sprout-invoices-pro/controllers/checkout/Checkouts.php:423 Stack trace: #0 /var/www/html/wp-content/plugins/sprout-invoices-pro/controllers/checkout/Checkouts.php(136): SI_Checkouts->complete_checkout() #1 /var/www/html/wp-content/plugins/sprout-invoices-pro/controllers/checkout/Checkouts.php(81): SI_Checkouts->handle_action('payment') #2 /var/www/html/wp-content/plugins/sprout-invoices-pro/controllers/checkout/Checkouts.php(70): SI_Checkouts->__construct() #3 /var/www/html/wp-content/plugins/sprout-invoices-pro/controllers/checkout/Checkouts.php(49): SI_Checkouts::get_instance() #4 /var/www/html/wp-content/plugins/sprout-invoices-pro/controllers/_Controller.php(491): SI_Checkouts::checkout(Object(WP)) #5 /var/www/html/wp-includes/class-wp-hook.php(324): SI_Controller::handle_callbacks(Object(WP)) #6 /var/www/html/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array) #7 /var/www/html/wp-includes/plugin.php(565): WP_Hook->do_action(Array) #8 /var/www/html/wp-includes/class-wp.php(418): do_action_ref_array('parse_request', Array) #9 /var/www/html/wp-includes/class-wp.php(818): WP->parse_request('') #10 /var/www/html/wp-includes/functions.php(1342): WP->main('') #11 /var/www/html/wp-blog-header.php(16): wp() #12 /var/www/html/index.php(17): require('/var/www/html/w...') #13 {main} thrown in /var/www/html/wp-content/plugins/sprout-invoices-pro/controllers/checkout/Checkouts.php on line 423