The Red flag on the appointment screen represents an Incomplete client record card set by the standards of the salon.

You can use this red flag as an indication that there is information missing from the clients record card so that when a staff member sees it on their booking they can ask that client for the information required.

You can mark the client's card as Completed by clicking Clients  (as shown in point 1. below) and then ticking the radio button next to Completed (As shown in point 2. below).  This will stop the red flag being shown for the client's future appointments