4xx Client errors
415 Unsupported Media Type
The server doesn't accept the request body's format.
Common causes
- A missing or wrong Content-Type header, like sending JSON without application/json.
How to fix it
- Set the Content-Type header to match the body.
Find out the moment your site returns 415
Spot Downtime monitors count this as down and alert you, since visitors see an error. (The public “Is it down?” checker treats 4xx answers from big sites as online, because many refuse automated requests.)