Is it possible the server is misconfigured, leading to a false 'client certificate required' 403 error in Postman?

Yes, it's possible. The server might be incorrectly configured to require a client certificate when it shouldn't, or the server-side logic might have a bug that incorrectly triggers the 403 error. If you've exhausted all client-side troubleshooting steps and are confident your certificate is valid and correctly configured, contact the server administrator to investigate potential server-side issues.