HTTP 411 status code indicates that a request lacks a Content-Length header.
Content-Length HTTP header contains the size of the request body (in bytes) and should be sent with all requests that have a request body. Typically, these are POST, PUT, and PATCH requests.
Content-Length: 42
Content-Length header is ignored when the data Transfer-Encoding header is present.
Try it yourself
Send a POST request to example.com with an empty body and without a Content-Length header, and you will receive a 411 Length Required status code:
curl --verbose -X POST https://example.com
Try resending the same request with a Content-Length header, and you will get a 200 OK response:
curl --verbose -X POST -H 'Content-Length: 0' https://example.com
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