Hello,
1) Make sure that OpenSSL system library is 1.0 or greater.
2) Contact your hosting provider and ask if there are no limits for the outgoing/ingoing connections. To activate theme your server should send the request to our server, our server checks the request and sends the response. Your server should get the response. If it does not work then there are some limits.
3) Check availability of 136.243.62.35 from your source IP address.
Regards