Version 3 of the ActiveCampaign API is structured around REST, HTTP, and JSON. API endpoint URLs are organized around resources, such as contacts or deals. It uses HTTP methods for indicating the action to take on a resource, and HTTP status codes for expressing error states. Resources are represented in JSON following a conventional schema.
Version 1 of our API is still available here. We have no plans to sunset version 1 of our API at this time and if we ever do, we will provide plenty of advance notice to our community.