Hello!

Yes, when Jot Server doesn't work, users can send and get messages, but it will work without realtime notifications. It means you will not be able to see that someone typing a message and there is no history update when someone sends message. Jot Server works to perform realtime update in the Messenger and it doesn't work because your server doesn't allow to connect to Jot Server. In most case it is because of closed port on your server for external connect. 

Provide me please with server url link which you put in Jot Messenger settings to Server URL textbox, i will check.