If you configured that Broadcast properly (ie. the other Topic indicates you installed MSTC) and still nothing appears, then Messaging Server is not working properly.
Although the “Connected” message is supposed to indicate that the Terminal is connected with the Messaging Server, it is not indicative of proper Messaging Server configuration. For example, the Terminal might be connected to itself rather than the “real global” service on the Server machine.
With those things in mind, best guess is that you have Message Server running on more than 1 Terminal, even if you believe this is not the case.
Turn off all Firewall programs, including Windows (Defender) Firewall.
Check Windows Services on all Terminals to ensure SambaPOS MessagingServer Service is installed and running on only 1 machine - the Server.
Check the Windows Tool Tray on the Task Bar on all Terminals to ensure NONE of them have a red apple icon in the Tray. If a Terminal has that apple, then it is running a Message Server in standalone mode. You need to avoid this on all machines, including the Server machine. Use the icon to terminate the program, and ensure your Terminals do not have that program in their Startup folder.
Check the SambaPOS Version on all Terminals to ensure they are all running v5.2.3. Double-click on the top-left of the title bar to reveal the version and build date.
Check the Clock on all Terminals to ensure they are all set to the proper date and time.