The deposit is the payment that actually holds the date, and it used to wait on you remembering to build an invoice after a signature you might not have noticed. Now the ask goes out with the good news, in one message rather than two — a bill arriving separately, seconds after “you’re booked”, reads as a catch.
An invoice for the deposit amount appears against the event, marked sent, and your client has a button to pay it.
Connect Stripe first. Without it the invoice is still raised and still emailed, and your client reaches a dead end trying to pay it — see Set up payments. The balance is separate and stays yours to send when your terms say so.