title: The 'Access-Control-Allow-Origin' header has been blocked by CORS policy
body: <p>I create API, BackEnd and Frontend website. </p>
  
  <p>I used Express for API, BackEnd - FrontEnd using ReactJs</p>
  
  <p>So in my local everything works. But when i deployed to server This error message show</p>
  
  <pre><code>Access to XMLHttpRequest at 'http://domain/headline' from origin 'http://domain' has been blocked by CORS policy: The 'Access-Control-Allow-Origin' header contains multiple values '*, *', but only one is allowed.
  </code></pre>
  
  <p>and</p>
  
  <pre><code>Access to XMLHttpRequest at 'http://domain/marketData/snack' from origin 'http://domain' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
  </code></pre>
  
  <p>in ReactJs im using axios for getting data.</p>
  
  <p>And in my nginx server i already set</p>
  
  <pre><code>location / {
          proxy_set_header X-Real-IP $remote_addr;
          proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
          proxy_set_header X-NginX-Proxy true;
          proxy_pass http://127.0.0.1:3001;
          proxy_set_header Host $http_host;
          proxy_cache_bypass $http_upgrade;
          proxy_redirect off;
          if ($request_method = 'GET') {
                  add_header 'Access-Control-Allow-Origin' 'http://domain';
                  add_header 'Access-Control-Allow-Credentials' 'true';
                  add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
                  add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
              }
      }
  </code></pre>
  
  <p>Did i missed something?</p>