Currently the workload compatibility API is a private API.
Please file a feature request to get the compatibility report API made public.
As a workaround you can use the Workloader tool or the C++ Absorption Toolkit tool to pull the compatibility reports. They are located on the tools page of the support portal.
https://support.illumio.com/tools/index.html
Direct links below
https://support.illumio.com/tools/c++-absorption-toolkit/index.html
https://support.illumio.com/tools/workloader/index.html