I briefly looked in the Tribler git repository, yes it looks like they modeled the api after uTorrent, but the source code on github goes back to 2012 before which it was svn. Definitely used an old version as template.
Sonarr rejects the api based on advertised version, not even sure if it’s actually reporting that old uTorrent version…
In any case, you’re out of luck.
We didn’t implement support for those older versions because those version do not easily expose the fields we require.
In addition, uTorrent has an api that goes against json best practices. To name something, it uses an array with values instead of a object with key-value pairs.
Basically it isn’t a full api but rather a backend for the webui and generally ‘not-fun’ to program an api client against.
Tribler should make a better api and ditch the current one entirely. In fact, they could probably benefit from looking at Transmission as example of a workable rpc/api. Or even the Deluge webapi. (which is written in python, btw)
Anyway, the Tribler sourcecode comes from <=2012, when it was probably less than a proof of concept focusing on the primary goal of the project.