Won't authenticate on Mobile using SPA app React/GatsbyJS configuration

I am having the same issue w/ iOS users…

User Logs in first time and it works
User returns or reloads the page and silent auth fails.
App asks them to login and they get redirected to Auth0
Auth0 returns immediately (because they are logged in)
Page reload effect when returning to app, state is not logged in because silent login fails
User clicks login again
(repeat…)

I am interested in trying #1 above. I have a paid plan. Not sure how to implement the “redirect only to a subdomain”.