From what I can tell, the "Request Ride" intent for Uber is broken (throws error on any request) and has been like this for at least 2 years.

The Ride Request API [1] seems closed off to developers now, too.

[1] https://developer.uber.com/docs/riders/introduction

Shortcuts was massively downgraded within one or two Apple-first releases (the original app was amazing, let me do local automations on the watch that included texting and API calls)