Thanks for the quick reply.
Here is the flow:
1. User a and user b communicate with messages.
2. A booking is completed. The booking confirmation contains the link to the parent message which now has fep meta ‘booking_confirmed’.
3. User a and user b can delete the message thread from the message box.
4. After message deletion, for either user, the message can be accessed from the booking confirmation. They have permission to view the message and can send further messages in the same thread.
Essentially, when a message is deleted by either user with meta ‘booking_confirmed’ it only means that they cannot see the message in the message box. Everything else is the same. It is more like “hide” message.