If the HTTP Method is not all upper-case, Nginx rejects the request and sends a 400 response along with its internal 400 HTML error page.
no details shown on “error_log info”
example: Link, LInK, SeaRCH, VeRB, etc … upper-case versions of those work, its jut the mixed case.
From the HTTP 1.1 RFC;
As far as I can tell, Nginx is doing the right thing according to the specification. If you disagree, you’ll have to explain what you think it’s doing wrong more clearly.
Edit: Yes, I agree with the answer from @JulianReschke, it should return a 501 status code, not a 400, good catch.