To Enable Chat, go to Classified Listing => Settings => Chat
The chat is between the buyer & seller. The users also have a chat menu to enable on the user dashboard my account menu

8.1) Regenerate Chat Table: If you want to regenerate previous chat table click here. It will remove all the chat history.
8.2) Chat: To enable a chat between the Buyer & Seller as well as the chat menu, check this checkbox.
Unread Message Email: Check this box to enable the first unread message to be sent as an email.
8.3) Delete Inactive Conversation: Set the number of days it takes for inactive chat messages to be delete. Leave it blank if you don’t want to delete inactive chats.
Due to the server database table structure, sometimes the chat data won’t save or show on the dashboard.
In this case, follow the instructions below:
1=>Ok go to your PHPMyAdmin backend and remove these two tables
wp_rtcl_conversations
wp_rtcl_conversation_messages
2=> Deactivate classified listing plugin
3=> Reactivate the classified listing plugin