The server is definitely up and running with people active on it, so this is some problem with your internet service provider, or you may be getting limited by your workplace or educational institute.
TPTMP v2.1.0 is out now. This is a REQUIRED update, and also requires TPT 98.0.
Changelog: 98.0 Support Add element negotiation, custom elements are now synced between clients if both users are running the same script Add /alpha command to control window alpha. Takes one arg between 0 and 255
If you get a protocol error while connecting, be sure to update tptmp in script manager, and then also update your game to 98.0 if you haven't already.