Related Questions:
Designate a primary contact for a booking
Make a contact primary
Procedure:
From the Booking Summary
Scroll to Contacts on the left-hand side of the Booking
Hover over the contact you wish to make the primary
Once complete, select Set Primary next to the name you wish to set as the primary contact.
Additional Information
The Primary Contacts information will be pulled into Invoice fields & also Documents, using Client merge fields.