Mark the project contact as 'inactive'
Make a project contact inactive to stop them from being sent any future created project documents, emails, or invoices. Contacts cannot be deleted from the project if they have been used as an invoice contact. Mark the contact as inactive to stop your team accidentally including the contact on future project communications.
Go to: Project > Project contacts tab and Select the check box(es) on the row left for each item you want to mark as inactive. Click the multiple rows action button and choose 'set as not active'.
The list refreshes and the now inactive item(s) are shown with a strike-out style applied. Update the list to use the 'active' filter 'all' option to see both active and inactive project contacts.
If the contact has not been included on any project communications like invoice, then they can be deleted from the project.
Stop the contact being used in the future by opening the contact record, and marking the entire contact as inactive.