Where does trackinklink come from?

Given that the tracking link in the API is a full URL to the carriers web site:
“trackingLink”: “https://www.fedex.com/apps/fedextrack/?action=track&trackingnumber=6789”
where does the first part of the URL come from? Does it need to be set by VELO when the order is fulfilled? Or is it part of the site setup?

I cannot imagine that, without using VELO that the site owner would have to supply this manually each time