As far as I am aware, there is no API. Any that exist (or existed) have been third parties which scrape the uplay accounts. You best avenue for support is with the 3rd party you are considering using, which I will guess is tracker.gg.
I would really pause before spending time building on top of this to be sure the data you can get is as detailed as needed, and how that might be impacted with the move from uplay to ubi-connect.
Okay, thanks. I guess I didn't realize it was not an official API. I didn't pay attention to the URL I'm calling but I now see it's tracker.gg. So what they list as the API is likely all there is. I wanted to see if I can get a list of players in our clan. I now have to maintain that list manually.
I'm using the API to get the overall play time of each player in our clan. Then use the differential on that from week to week to tell who is playing and who isn't so I can remove inactive players. I'm not trying to do anything extensive.