the ticket that we did but in the middle of the way the ticket was changed by the agent, so the agent who did the change did the first agent not be able to post another reply?
I haven't the foggiest idea what you are asking.
I HAVE A PROBLEM WHEN TICKETS are assigned to agent 1 but after that the agent is replaced by agent 2, can agent 1 still communicate with the client?
If the ticket is in a department that Agent 1 has access to, then yes they can respond to the ticket (which responds to client). If it is not, then they cannot.
