location /api/ {
    expires -1;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_pass http://api:3500/;
}

Access to XMLHttpRequest at 'https://mysite.com:2053/socket.io/?EIO=3&transport=polling&t=NAKO6CN' from origin 'https://mysite.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.