The broadcast message would distribute a message to all terminals.
That wouldn’t be a message that pops up - more of a trigger/kick which you need to setup a rule to listen for broadcast message and react accordingly.
To send to a specific terminal you would have to filter them by way of some sort of reference and constrain the pop up at the receiving end in the rule that fires the popup.
I think you would have at add a ‘reference’ to the broadcasted message being sent.
Such as TERMINAL1 - MESSAGE and the rule to look out for broadcasts is filtering for that with ‘contains’ TERMINAL1 and map that rule to that terminal.
You might been a separate rule for each terminal mapped accordingly.
This is not something I have done but pretty sure this would work.
Bit I’m not sure is how best to Deal with the ‘terminal reference’ at the sending end.