First, you need to fulfill the order in Bigcommerce .
If you have a tracking number, you need to provide both the Tracking number and the Shipping carrier, Most marketplaces require both.
The tracking info must be provided at the same time when you mark the order as fulfilled. Otherwise this info will not be retrieved by us and not updated on whichever Marketplace
See below the Order Fulfillment screen in Bigcommerce
Also, if your customer doesn't know both of these they are not able to track the package.