They accept, and the booking is already built.
Already on
Accepting a proposal used to mean a message you had to notice, then twenty minutes of typing the same details into a new event, a new contact and a new contract. All three already existed in the proposal they just agreed to.
An email lands in your inbox and a notification appears in the app. Open the event and the draft contract is there.
If they DECLINE instead, the proposal is marked declined and the lead moves to Lost automatically, so you stop chasing a decision that has been made. They are not asked to create an account in order to say no.