File Content: bootstrap.php <?php mc4wp_register_integration( 'ninja-forms', 'MC4WP_Ninja_Forms_Integration', true ); if ( class_exists( 'Ninja_Forms' ) && method_exists( 'Ninja_Forms', 'instance' ) ) { $ninja_forms = Ninja_Forms::instance(); if ( isset( $ninja_forms->fields ) ) { $ninja_forms->fields['mc4wp_optin'] = new MC4WP_Ninja_Forms_Field(); } if ( isset( $ninja_forms->actions ) ) { $ninja_forms->actions['mc4wp_subscribe'] = new MC4WP_Ninja_Forms_Action(); } } Submit