Rest API return duplicate header

I try to use the REST API to retrieve tickets in Zendesk. Our client has a verifier of HTTP responses. But the REST API always returns some duplicate headers, which makes our verifier fail. Here's the screenshot of a postman sending the basic tickets query.

According to the HTTP RFC https://datatracker.ietf.org/doc/html/rfc2616#section-4.2    Headers are case-insensitive.