Tracking numbers are posted to eBay, with carrier links, once you dispatch an order within the system.
To make sure your tracking links are displayed correctly on customer’s eBay accounts, the Third Party Name of your service and rate needs to match one of eBay’s service codes.
You can define this under each service in the system by navigating to Setup & Tools > Shipping.
Select Shipping Services & Rates and then choose the related service and rate table.
Entering the service code into the Thirdparty Name field.