There are two distinct environments available for the API. The production environment is the one your production applications should use, but a sandbox environment is also provided for testing your integrations. The sandbox is an environment completely isolated from production, but some of its data is based on the data from the production environment.
Authentication credentials (your token and secret) are enabled on either sandbox, or production, but not both.
The following are the hostnames that should be used for each environment.
It's especially critical that any testing of non-
GET requests be done in the sandbox environment to avoid making unintentional or detrimental changes to production data.