500 internal server error with long urls when using nginx as reverse proxy

I am receiving a 500 internal server error when opening a long url with several GET parameters that is about 2400 or more characters. The long url is for Google recaptcha, that adds g-recaptcha-response get parameter, something like:

https://example.com/?g-recaptcha-response=xxxxlongdataurlxxx&action=validate_captcha

When connecting to the webserver after nginx reverse proxy, I receive a 500 internal server error for such long urls. If I connect without nginx reverse proxy, everything is fine.

So there are limitations in webserver <-> nginx proxy server interaction (both of them have centos 7 installed). In both nginx main config files (/etc/nginx/nginx.conf) i added/modified strings with parameters:

client_header_buffer_size 8k;
large_client_header_buffers 4 16k;

But the problem remains.

What can I do to solve the problem?

Use post instead of get because Google recaptures support post.

and try client_header_buffer_size 16k; large_client_header_buffers 8 64k;