That is correct that the appID is only available the first time (for now, this is still a beta functionality so things could change). This is why the step says to save this ID. I will have to ask how to retrieve it another way, I’m not sure at the moment.
You also need the appID again for the testing addToCurrentCart as shown here: https://www.wix.com/velo/reference/wix-ecom-backend/currentcart/addtocurrentcart?branch=autodocs-wix-ecom-backend
specifically, when testing a custom catalog you must add appID here in the line items
I will get back to you about how to get the appID if you have not saved it after the initial step and see if having that helps get this working