CORS with ionic run -l -c, proxy not working

Using ionic emulate ios, API requests are able to reach the API on my local machine just fine. However, ionic emulate ios -l -c causes the app's API requests to reach the server in the form of preflight requests:

OPTIONS /api/user/get/profile_mob 200 1.68 ms

ionic.project uses a proxy:

"proxies": [
  {
    "path": "/api",
    "proxyUrl": "https://dev.app.com/api"
  }
]

nginx.conf below:

location /api {
  add_header              'Access-Control-Allow-Origin' '*';
  add_header              'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, PUT, PATCH, DELETE';
  add_header              'Access-Control-Allow-Credentials' 'true';
  add_header              'Access-Control-Allow-Headers' 'X-Requested-With,content-type';
  proxy_redirect          off;
  proxy_http_version      1.1;
  proxy_set_header        Host $http_host;
  proxy_set_header        X-Scheme $scheme;
  proxy_set_header        X-Real-IP $remote_addr;

  proxy_set_header        Upgrade     $http_upgrade;
  proxy_set_header        Connection  "upgrade";

  proxy_hide_header       X-Powered-By;
  proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
  proxy_pass              http://localhost:3003;
}

From my readings, configuring the proxy and adding proxy should have fixed the problem. What else can I try? Any help would be appreciated.