How do my customers get their tracking numbers?
So long as your customer has provided a valid email, once you select 'Fulfill orders' at the end of the fulfilment process within Addition, the app will trigger two requests - one request to Shopify, and one to request Australia Post to "send tracking emails".
The order Timeline in Shopify will update as below, as a confirmation that Addition has triggered the Shipping confirmation, e.g.
*Shipping confirmation template is in Shopify Settings > Notifications section
While Australia Post is triggered to send their standard "Delivery is coming" email, e.g.