Working with Reservation Policies and the vRA REST API

Using vRA 6.2.1. Looking to be able to create a Reservation Policy via the REST API, initially though I thought I would try listing the existing Policies.

This page documents the GET request needed to list them, basically:

GET: https://vraappliance/reservation-service/api/reservations/policies

Accept: application/json

Authorization: Bearer AuthenticationToken

I know the REST API is working and my token is good because I can successfully make other calls, however this one returns:

{

  "errors": [

    {

      "code": 50505,

      "message": "System exception.",

      "moreInfoUrl": null

    }

  ]

}

Any ideas?