Hi @Marie-Claire0
They actually already have this type of notification that gets sent out!
Once your client books with someone else, they are given the option to send a mass-message to all their pending inquiries that it "will no longer be needed" & automatically cancels their inquiry.
Not sure if this is just a option or an automatic type of thing, if the client opts to not send it.
I only know because of when I made multiple inquiries and booked with one, I was given the option to, and it sent them out!
..was definitely convenient!
Hope this helps!
Antonella