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://email@example.com where firstname.lastname@example.org is your actual Fastmail email address (that doesn't necessarily end with @fastmail.com). So if your email is email@example.com your server would be: https://firstname.lastname@example.org
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