So, it appears the connector works then, but there's probably no packages to index. This is because telerik uses scoped packages.
Unfortunately, the npm API does not support listing or searching scoped packages at all. That is to say, there is simply no way for us to ask that API endpoint at telerik what packages exist there. So, this is by design… albeit a poor one by npm.
You will find the same is the case if you try to search for a scoped package on npmjs.org, for example this one: https://www.npmjs.com/package/@types/react
So, in this case, you won't be able to find telerik packages in a search or from the UI. You can only know the exact name.