If you have specific questions about using the HubSpot APIs, or would like to report a problem with any of the HubSpot APIs, your best resource is HubSpot's Developer Forum.
This forum is a community of HubSpot developers and HubSpot users.
The documentation for all of the HubSpot APIs is located at http://developers.hubspot.com.
Specifically, you can find a list of all of our API endpoints at http://developers.hubspot.com/docs/overview. Each endpoint has its own documentation page detailing the usage of the endpoint.