we are building a connector App that will just work in the background and sync some catalog data we have, with our user's Shopify catalog. So essentially the only reason we have the app is to allow for some data sync between our Web site and the users Shopify store.
We wonder if in this case we also need to use the Billing API? since users will not actually interact with the app at all, and also we plan to not charge anything for this connector app from our users
for reference this app will be similar to the quickbooks connector app:
We are currently in the same situation, where we have our App complete and ready for approval, but we have been exchanging e-mails with Shopify because they do require us to use the billing API, while we provide our App as a bridge between Shopify and our platform, not charging anything for the app usage.