What is it?
In detail: Custom Region is a suite of APIs that can be used to create a custom region and associate to your desired country and/or airport codes. Your custom region can then be used as a filter in your Destination Finder API request (e.g. region=NewZealandPacific).
NOTE a given custom region (and all subsequent customizations) is mapped to and accessible by a single Pseudo City Code (PCC) in your token credentials when you get a token to call REST APIs, and cannot be shared or used by any other PCCs.