I'm trying a simple request to sandbox: https://sandbox-api.uber.com/v1.2/requests/current
with token generated with my account: tristan.tran89@gmail.com and get a 403: forbidden error.
Same request with a different account does not return a forbidden. Can someone please verify why it's being blocked on my account?
That is typically what the 403 error indicates. Strictly it is saying that the token you sent does not have access to the resource. This could mean it's been corrupted, it expired, or the user revoked access.
If the current application is the one that booked the trip then requests/current should be able to be accessed.
In your case, you are calling GET v1.2/requests/current with an access token that has the request scope but not the all_trips scope. That means that the endpoint will respond with the current trip only if it was booked by your application. In the case that the user is on a current trip but it was booked by another application or the Uber app, you will get a 403. In the more common case that the user is not on a trip at all, you will get a 404.
If you wanted to be able to give status updates for any trip that a user takes, you would want to get the all_trips scope during OAuth.