There are two non-production environments that can be used for the testing of API integrations for both POST and GET requests. Login details are the same as those given for the Production environment.
The Staging environment is a copy of the Production environment, and is only changed prior to a software release to ensure that release doesn't cause any issues when deployed to Production
The UAT environment is used to test software changes before they are released to Production. This environment can differ substantially from Production, depending on what software changes are being developed.