Availability is the whole product
Offering open slots looks like the easy part and is the hard one. A genuinely bookable slot requires five things to be simultaneously true: the shop is open, that technician is on shift, that technician is qualified for that service, the service's real duration fits before the next appointment, and any add-ons have extended that duration.
Tools that approximate this produce slots a human then has to correct — which teaches your team that the calendar cannot be trusted, and sends them back to the phone and the paper book.
We resolve all five on the server before a time is ever offered. It is the least visible part of a booking system and it decides whether staff actually use it.
