Login From Custom Form CORS Issue

Getting a CORS issue trying to login from custom form following along from A Quick Guide to React Login Options | Okta Developer.

Have cors turned on and tried to open it up to even allow https://*. No love there.
Though maybe that was too permissive and added just the domain to test from here (Enable CORS | Okta Developer) and that doesn’t work either.

Logging in from Okta widget with redirect works absolutely fine.

What endpoint is returning the CORS error and for what domain? Do you have a screenshot of the error?