We are a small startup with our own billing system set up. We are trying to get our customers on Shopify, where we would charge a small 17p fee on every transaction. We were hoping to do this via a tracking webhook where each sale would be recorded on our own system, then we would bill them from there.
However we are wondering what the requirements to use the Shopify Billing API are. Would we be required to charge this 17p on the actual transaction (rather than at the end of the month on our own billing system as a cumulative amount) using the Shopify Billing API? Or are we allowed, if we were to publish a public app to the Shopify App Store, to bill them ourselves on our own billing system?