I was trying to implement Uber API into an android app. I went through the documentation: https://developer.uber.com/docs/riders/ride-requests/tutorials/api/android
What is redirect_uri? How can I create redirect_uri for an android app?
It's implemented by OAuth2 APIs and essentially means the url where the provider (in this case Uber) redirects the status of the auth request on successful or failed authentication. See OAuth2 spec for further info.
In your case it could be your server where you store the access token of the user in your database