_redirects not working - new to netlify

I am hosting a custom domain on netlify and I’m deploying a react site using the Okta Sign In Widget trying to authenticate to an OIDC app. When I click on the Okta chicklet from with in the Dashboard I get this error:

I get directed to this URL: https://www.ironcove-test-one.com/implicit/callback

I added a _redirects file with this content(using the netlify redirect docs):

/* /index.html 200

If I remove the implicit/callback from the url the site works as expected. If I add a bogus URL like https://ironcove-test-one.com/xxx the URL get redirected to the index.html per the redirects rule.

The error in network tab shows a POST. Netlify doesn’t allow HTTP posts. Any guidance on how I can solve this?

Where is the POST supposed to go? Presumably some other service, not Netlify? As you mention, we wouldn’t handle a POST that is trying to do anything other than a form submission to a predefined (at build time) endpoint, and that site has no forms defined, so I’d say behavior is correct even if not desired.