I am not sure if this is helpful, but thought I'd post the PHP warning to identify code tweaks for a future update. Please let me know if this is not helpful.

I am running Zen Cart v.2.1 and PHP version 8.3

The warning I receive is

PHP Warning: Undefined array key "action" in /includes/extra_cart_actions/sfl_actions.php on line 17.

Again, just trying to help for future plugin updates....as this warning does not cause any problems with how the plugin functions or operates for the customer.