HTTP status codes / 4xx — Client error
415 Unsupported Media Type
What it means
The server cannot handle the request body's format, as declared by its Content-Type.
What causes it
Sending JSON with a text/plain content-type (or vice versa), form data where JSON is expected, missing multipart boundary.
How to fix it
Set the Content-Type header to exactly what the API expects — application/json is the usual answer. For file uploads, let the HTTP library set the multipart header itself.