The Happeo API works on top of HTTP, uses standard HTTP verbs, accepts JSON-encoded body in requests and returns JSON-encoded responses. It is technically not a REST API, but those familiar with REST should find it quite natural to use.
The base url for the API is: https://api.happeo.com
Use HTTPS and SSL when calling all methods.
You need to be a customer or partner of Happeo to be able to use the API. You will also need to sign in with your Google Account into Happeo and create a system account to get an apikey to use the APIs.
The authentication to the API is done with the apikey and the actions in Happeo are done as the system account user the apikey belongs to.