I tried to make a payment using the web self serve portal but my browser stopped me. This occurred after I entered the payment amount (first step, pressed a button that says "Next"). While using an up to date version of Chrome, I got a "Your connection is not private" error page with an error of NET::ERR_CERT_AUTHORITY_INVALID.
Here's the advanced message:
This server could not prove that it is pay2.koodomobile.com its security certificate is not trusted by your computer's operating system. This may be caused by a misconfiguration or an attacker intercepting your connection.