Content-Type / MIME Type
The header that tells the other side what format the body is in, like application/json or image/png. Wrong label, unreadable data.
See it
What it is
A MIME type (officially a media type now) is a short label like 'application/json', 'image/png', or 'text/event-stream' that says what format a chunk of bytes is in. The Content-Type header attaches that label to a body: on a request it means 'here is what I am sending', on a response 'here is what I am returning'. Its cousin Accept says 'here is what I would like back'.
The four you will actually meet: 'application/json' for API payloads, 'application/x-www-form-urlencoded' for classic HTML form posts, 'multipart/form-data' for file uploads, and 'text/event-stream' for server-sent events. Add 'charset=utf-8' on text types so accented characters survive the trip.
Gotcha: a mismatched Content-Type is a common cause of an empty req.body and a baffling 400 or 415. If you JSON.stringify a body but leave the default header, the server's JSON parser never runs and your handler sees nothing. Second gotcha: never echo back a user-uploaded file's claimed type. Browsers will sniff and execute HTML you serve as an image, so pin the type server side and send 'X-Content-Type-Options: nosniff'.
Ask AI for it
Audit and fix Content-Type handling across this integration: send 'Content-Type: application/json; charset=utf-8' with every JSON request body, send 'multipart/form-data' only for file uploads (and let the runtime set the boundary), set an explicit 'Accept' header on outbound calls, and check the response Content-Type before parsing so an HTML error page never reaches JSON.parse. On any endpoint that serves user-uploaded files, set the type from server-side detection and add 'X-Content-Type-Options: nosniff'.