415 4xx RFC 9110 §15.5.16

Unsupported Media Type

Request's Content-Type isn't supported by the endpoint.

What HTTP 415 means

RFC 9110 §15.5.16. The endpoint supports specific Content-Types (e.g., only application/json) and the client sent something else. Usually missing or wrong Content-Type header on the client.

Typical causes

Missing Content-Type header
Sending form data to JSON-only endpoint
Wrong charset