Init() attempts to call a non-static function

[rtpHarry]

I used your code to initialise my plugin (thanks) and noticed that I got errors for this:

https://github.com/NickGreen/automatewoo-order-add-product/blob/main/class-automatewoo-order-add-free-product.php

The error was:

2023/11/29 04:24:03 [error] 124990#124990: *1562611 FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method RunThings_AutomateWoo_WooCommerce_Store_Credit::register_action() cannot be called statically in /www/knepp_839/public/wp-includes/class-wp-hook.php:324

I had to make the register_action static as well.

Maybe it was one of those silent errors, or has become fatal with a newer version of PHP, anyway, I thought I would give you a heads up in case you have this running on any of your sites.