Why can't Mint connect to the gateway?
There are a couple of possible reasons. You could be experiencing an intermittent network failure between your server and haveamint.com. In this case the only option is to wait it out and try again later.
Other potential causes include: your host may not have the cURL PHP library installed, they may have crippled PHP’s native
fsock family of functions, or they could be using a firewall that prevents outgoing traffic from your server. Your Mint installation must be able to connect to haveamint.com in order to activate (during installation) and to check for updates. You will need to work with your host to resolve the problem.
This issue is identifiable before purchasing Mint using the required Mint Server Compatibility Suite (and therefore, unsupported).