Vyte has an easy CalDAV integration that will let you connect your Fastmail calendar to Vyte. With this integration booking appointments on a Fastmail calendar will be super easy. You'll also be able to easily schedule meetings with Fastmail and Vyte.

To add your Fastmail calendar to Vyte you will need 3 pieces of information:
   1. Your server: https://caldav.fastmail.com/dav/calendars/user/user@fastmail.com where user@fastmail.com is your actual Fastmail email address (that doesn't necessarily end with @fastmail.com). So if your email is john@fastmail.in your server would be: https://caldav.fastmail.com/dav/calendars/user/john@fastmail.in
   2. Your username: that will be your Fastmail email address
   3. Your password: You will need to generate an app password on Fastmail for Vyte. This Fastmail help center article will guide you through Adding a new third party app to get a password for Vyte.

Once you have gathered these 3 items, you can add your Fastmail calendar to Vyte as a CalDAV calendar by following this tutorial: Connect a CalDAV calendar to Vyte