Applying cors on my nginx returns 500 status code

I have a nginx config with cors headers:

 location / {
    include proxy_params;
    proxy_pass http://unix:/home/gftpl/myweb/web.sock;
    if ($request_method = 'OPTIONS') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Methods' 'GET, PUT, OPTIONS, POST, DELETE';
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization,X-Amz-Date';
        add_header 'Access-Control-Max-Age' 86400;
        add_header 'Content-Type' 'text/html; charset=utf-8';
        add_header 'Content-Length' 0;
        return 204;
    }
    if ($request_method = 'PUT') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Methods' 'GET, PUT, OPTIONS, POST, DELETE';
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization,X-Amz-Date';
        add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
        add_header Access-Control-Allow-Credentials "true";
    }
    if ($request_method = 'GET') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Methods' 'GET, PUT, OPTIONS, POST, DELETE';
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization,X-Amz-Date';
        add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
        add_header Access-Control-Allow-Credentials "true";
    }
    if ($request_method = 'POST') {
        add_header 'Access-Control-Allow-Origin' '*' always;
        add_header 'Access-Control-Allow-Credentials' 'true';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, PATCH, PUT, DELETE, OPTIONS';

add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
    }
}

and when I test this on test-cors.org POST Request it send me Error Status Code 500.

Did I made mistake in applying cors or?