To sync your products from Zetpy to Shopify, you need to create Category (Collection) in your Shopify store. Only then you can add product in Shopify plug-in.
Only NEW products from Shopify online store will be imported to Zetpy. The existing products in Zetpy will not be imported again.
Shopify Private apps are deprecated. However, it still can be used for the existing Zetpy user. From now on, all new users have to use the new Admin API Access Token to authorize the Shopify account.