onsync() plugin type is called after an item in the outbox is succesfully synced (or has an error). See @wq/outbox for the description of the available attributes.
Note that this function will be called each time an item is synced, regardless of how the item was created. If you have custom code that calls
outbox.save() directly, you can use
outbox.waitForItem(id) instead of this plugin type.