Please click here for our current API documentation: developers.gohighlevel.com
Going forward we are moving to an OAuth based API, these docs can be found here: https://highlevel.stoplight.io/docs/integrations
As of now not all end points have been moved from the original API to the OAuth flow, but check with the oauth flow docs first and use that API if the endpoint exists.
For any question please join the developer Slack group here: https://join.slack.com/t/ghl-developer-council/shared_invite/zt-puqvvhdu-lpgk5YaijZfe9XT_b1LEpg