To confirm, you are trying to hit this endpoint to retrieve a public key, correct?

In order to get this endpoint to publish/return your public key, you will need to either import or generate a key pair. I would review whether you are importing an existing key pair or generating a new one here: https://fusionauth.io/docs/v1/tech/core-concepts/key-master#importing-vs-generating

Have you done this step yet? If not, once the pair is imported/generated correctly, this endpoint should return your public key.

If it's still returning an error, please let us know.

As for the @JSONResponse error, we should be handling that and you should be getting this response when hitting the same endpoint with the applicationId.

{}

I opened a bug here if you would like to track it. https://github.com/FusionAuth/fusionauth-issues/issues/1918

source: https://fusionauth.io/community/forum/topic/404/i-imported-a-public-key-and-am-not-seeing-the-kid-in-the-jwks-endpoint

Thanks and happy coding,

Johnathon