Hey @jordanurbs, you are not the only one It should be much better documented.
Anyhow, here it goes:
To connect Zapier to a self-hosted Cal.com instance, follow these steps:
TL;DR
Invite Link == Whatever sequence of random numbers and letters you want (aka API Key!)
Note that the invite link / API key
Create an app for the connection in Zapier's dev account
Log in to your self-hosted Cal.com instance as an admin.
Navigate to the settings/admin/apps section of your instance
Enable the Zapier app in your Cal.com instance and set the necessary app keys
Generate an API key specifically for Zapier integration (https://<yourinstance>/apps/zapier/setup)
In Zapier, create a new Zap and select Cal.com as your Trigger app
When prompted, enter your unique API key generated from your self-hosted Cal.com instance
Test the trigger to ensure the connection is working correctly
https://github.com/calcom/cal.com/blob/main/packages/app-store/zapier/README.md
https://developer.zapier.com