Hi casikring ,
Thank you very much for your reply. Sure the answer you got from them was expected. This is a never ending issue with plugins. They will not adapt and unfortunately, we would not either, unless it is a plugin with at least 100k of users or widely used official WC extension.
Imagine we spend days or weeks to make things work (costing the fix several thousand euros) and then they change a code and all work is wasted. You would need a developer to keep this compatibility ongoing.
You have 2 choices here, one is to pay a 3rd party developer or second to choose either of the plugins and delete the other one. If you decide to delete ATUM PL, please open a private ticket.
Hope this makes sense.