Use cloudflare proxy for authenticated api

Here is the response I get when doing a GET, with CORS so it does an OPTIONS request first, from my web application:

Request URL: https://api.primordial-software.com/budget
Request Method: OPTIONS
Status Code: 521

I get the same 521 error when going to the proxied domain in a browser (I’ve re-enabled the proxy so you can see the error now if you go to the domain): https://api.primordial-software.com/

My origin is returning this to cloudflare:

Request Url: https://api.primordial-software.com
Request Method: GET
Status Code: 403
Body: {"message":"Missing Authentication Token"}