Nginx if cookie exists, use proxy, if not, run php to create cookie and check again

I'm trying to create a condition with nginx that if a cookie does not exists, the nginx run index.php to create the cookie, and if a cookie exists, then the nginx goes to proxy.

How I can do this? I'm tried like this:

location / {

  if ($cookie_test = false) {
     try_files $uri $uri/ /teste.php?$args;
     include /etc/nginx/fastcgi_params;
     fastcgi_pass 127.0.0.1:9000;

  } else {

       add_header 'Content-Type' 'application/vnd.apple.mpegurl';

       proxy_set_header        X-Real-IP       $remote_addr;
       proxy_set_header        REMOTE_ADDR     $remote_addr;
       proxy_set_header        Host            $host;
       proxy_redirect          off;
       proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
       proxy_connect_timeout 90;
       proxy_send_timeout 90;
       proxy_read_timeout 90;
       client_max_body_size 10m;
       client_body_buffer_size 128k;
       proxy_buffer_size 4k;
       proxy_buffers 4 32k;
       proxy_busy_buffers_size 64k;

       proxy_pass https://127.0.0.1:8080;

  }
}

but getting this error:

"try_files" directive is not allowed here