There are a few ways you and your clients can chat using Travefy and Trip Plans.
Advisor Option: Trip Builder
Inside the trip builder, you're able to access the discussion panel here.
Advisor + Client Option: Web Link - Itinerary
If you're viewing an itinerary with a web link such as https://travefy.com/trip/6yw9rqwxbjgsqz2adc9gv6qy9ln5j2q, there will be a chat icon off to the right of your screen.
App Options: Travefy Pro (for the advisor) and Trip Plans (for the traveler)
What about turning the messaging feature off?
To do that, you can follow the instructions here.