I was able to figure out the setup, but it is a fairly complicated process.
Since there is no existing module with access to create event scope, you need to set up an HTTP (make an OAuth 2.0) module and then click on "Add Connection."
Open a new tab and visit GoHighLevel Marketplace. You need to create your own private app and give it access.
In your app, you need to add scopes (calendars/event.readonly, calendars/event.write), and create a client key.
The Redirect URL should be set to
https://www.integromat.com/oauth/cb/oauth2 (not make.com).
There is no need to set up SSO. After that, just save it.
Now, go back to Make and set up the connection.
Authorize URI should be set to
https://marketplace.gohighlevel.com/oauth/chooselocation
Token URI should be set to
https://services.leadconnectorhq.com/oauth/token
Add both scopes, and then add the Client ID and secret key.
Click on ‘Show Advanced Settings’ and set the scope separator to SPACE (this is important if adding multiple scopes).
Verify the connection, which will open a new tab with your GHL account. Just follow the prompts.
After following these steps, the connection is verified. Now, you can follow the API docs for 2.0 to set up appointment booking.
Major Note: The API you request from this connection will only work if you are on the $497 plan(GHL is being Greedy)
Personally, I do not think it is worth it. You are better off setting up cal.com or Google Calendar and syncing that with HighLevel.
https://cdn.discordapp.com/attachments/1249779895761109022/1252428347066159104/f6163c873a904f818884bbd8d2b4e210_1.mp4?ex=66722e4a&is=6670dcca&hm=4b558f7bef3bbbdda91ad9ad26f7e4d9c9b72f1f1dac7806eab5109add6a1571&