The mentioned error is unique to Firefox, please provide the error other browsers get. I can reach the x12 server without any errors.
In addition to what the link references, some browser extensions or even firewall software can also interfere with reaching it, in addition to some browsing...
You should see a pay now button when logged into the account panel at https://x10hosting.com/panel/invoices if this is your first payment.
All renewals are handled automatically through your PayPal account as it is a subscription service.
The coupon code X10FREE75 is still active.
Towards the free logo, it is hard to say as their website's front page says $0, limited time only, but then $5 as you attempt to go through the process, someone likely just didn't update the main page