How to fix nginx throws 400 bad request headers on any header testing tools?

Question

I have my site which is using nginx, and testing site with header testing tools e.g. http://www.webconfs.com/http-header-check.php but every time it says 400 bad request bel

Answer 1

When nginx returns 400(bad request) it will log the reason into error log, at "info" level and take a look into error log when testing.