HTTP 505 HTTP Version Not Supported indicates the server (or an upstream dependency) failed to fulfill a valid request. Treat it as a reliability signal: capture evidence, attribute the failure, and apply safe retry and backoff based on idempotency.
Response includes the status code, standard headers (including Content-Type), and a small diagnostic JSON body describing the request and returned status.
curl -i "https://httpstatus.com/api/status/505"