Zapier confirmed they are using the V1 / 1.0 API for their integration with GHL. I discovered this when the "API Request" action was failing in a zap because I was using an API 2.0 endpoint.

There is a community thread in Zapier with others who are having the same trouble and similar questions:

Two questions from me:

1) When will GHL transition the Zapier integration/app to API 2.0? This would be helpful to know for business planning.

2) What is the simplest way to call the 2.0 API for those who don't have a large enough business need to justify building out the infrastructure to support ouath tokens that expire every 24 hours?

Regarding question 2 — there is feedback from a few folks on this forum disliking the requirement to create an app and having to wait a few days to a few weeks for approval for a simple integration and furthermore needing to build out infrastructure to refresh and store new oauth tokens every 24hrs (https://ideas.gohighlevel.com/apis/p/do-not-deprecate-the-v1-api-ever).

For those of us looking to quickly build simple integrations using tools like Zapier, it would be helpful to either have the Zapier app updated to reference API 2.0 (and support the "API Request" action) to avoid problems down the road with API 1.0 depreciation that could risk elements of our business, or have a more simple way (i.e. not needing to build out infrastructure to refresh and store new oauth tokens every 24hrs) to interface with the API 2.0 using webhooks via Zapier or similar tools.

Thank you in advance for the consideration and help.