What it means
The server refuses the request because the body's media type (Content-Type) or encoding is not supported.
Common causes
- Sending JSON without Content-Type: application/json
- Form-encoded body to a JSON-only API
- Unsupported Content-Encoding such as brotli on upload
How to fix it
As a client or visitor
Set the correct Content-Type header for the body you send, and match the format the API documents.
As the site or API owner
List accepted types in Accept-Post or Accept-Patch, and give a clear message.
Example response
HTTP/1.1
HTTP/1.1 415 Unsupported Media Type
Date: Tue, 07 Oct 2025 09:30:00 GMT
Server: nginx
Accept-Post: application/json
Content-Type: application/problem+json
{
"type": "about:blank",
"title": "Unsupported Media Type",
"status": 415,
"detail": "Send the body as application/json."
}Specification
FAQ
› Why does fetch() get 415 with a JSON body?
fetch sends text/plain for string bodies unless you set headers: {'Content-Type': 'application/json'}.
› 415 vs 400?
415 is specifically the wrong body type; 400 is a malformed request in general.