You can fully automate many routine tasks between PlentyONE and Shopify by setting up so-called event actions.

The principle behind this is simple: you specify that a certain event in PlentyONE (e.g. "Order has been shipped" or "Return has been created") automatically triggers a suitable action in Shopify (e.g. "Notify customer of shipment" or "Initiate refund").

You can find everything you need for this in your PlentyONE system under the menu Setup > Orders > Events. The specific actions for Shopify can be found when creating an action in the folder Plugins.