Hello,

With my ACMEv2 client implementation  https://github.com/bruncsak/ght-acme.sh I got the following error when trying to retrieve the KID:

HTTP/1.1 400 Bad Request

{"type":"urn:ietf:params:acme:error:unsupportedContact","detail":"The contact is malformed. Supported schemes: [tel:, mailto:]","code":400,"message":"UNSUPPORTED_CONTACT","details":"HTTP 400 Bad Request"}

The section 7.3.1 of RFC8555 is rather precise that:

   The body of this response represents the account object as it existed on
   the server before this request; any fields in the request object MUST
   be ignored.

Your code is checking the body of the request, what is not supposed to be done. I already implemented a workaround in my client, but you may wish to fix that in the server code to avoid the same issue with a different ACME v2 client.