Ask HN: Scheduling software to manage appointments of multiple employers

I am in charge of technical team for telehealth startup where we manage appointments between patients and hundreds of medical staff under our payroll.

We have been looking at SASS product to replace our in-house appointment system. We would not like to build calendar UI if we can find some plugin solution that works. Also it needs to provide API so our apps can talk to it.

We looked at a few like Calendly but those services seem to mostly geared towards personal appointments. There is no easy way to track, view and modify appointments of all staff. Is there a SASS product that would meet our requirements?