The best alternative to Roproxy is to self-host your own. Relying on other people’s Roproxy servers inherently opens you up to errors once they decide they no longer want to maintain it.
This tutorial should provide the best way to make your own Proxy for free & with minimal latency.
That said, it looks like roproxy.com is currently still working, so your issue is not Proxy-related. The /bundles endpoint seems to accept an item ID from the catalog and will show the bundles associated with that item. For example, Blue Collar Cat (Bundle ID 182), won’t work. But Blue Collar Cat Right Leg (Asset ID 146176511) will display the information of the bundle associated with it.
Oops. I was sending the bundle id, not the bodypart of the bundle. I’m going to see now, also thank you very much for the big clear and detailed answer!