I’ve made some progress. I now realize the reason this does not work is because I am receiving an access token as an opaque string rather in the JWT format. This is likely because I have not set the ‘audience’ parameter for my API above when I login. Set the Access Token Format. As far as I can see there is no way to set the audience parameter using the Auth0Client.
Given this, my solution will be to follow this Quick Start Guide: Mobile Login Flow Quick Start Guide