497 Plain HTTP Request Sent to HTTPS Port

Unofficial · nginx

A plain HTTP request arrived on a port that expects HTTPS. It can be caught with error_page; the client is sent 400.

Class
4xx Client Error. The request has a fault, or cannot be met as sent.
Registered
No. nginx sends it, and it is not in the IANA registry, so other servers may mean something else by it.
References
nginx

Every 4xx code

All HTTP status codes, in one table