So I setup a test idp setup at https:localhost:3000. For a while the process was going smoothly and then I began setting the logged in header in the accounts endpoint and now fedcm no longer calls my idp at all. If I change to a different URL like localhost:3002 it will call it just fine and report errors etc.

I've been using this guide for debugging which is how I was able to track the network requests. https://privacysandbox.google.com/cookies/fedcm/setup