Create VPG for VCD to VCD using API

I got a very strange problem to create VPG using APIs, Tried every thing i could but still get same error,
i am using zerto v6.0

i tried to create VPGs for VCD – VCD scenario

method 1. created skeleton Template and added  the data and when i post to https://zvm_ip:port/v1/vpgSettings,
i get error :400 {“Message”:”Object reference not set to an instance of an object.”}

where as when tried to create empty VPGs with out data, it does create one.
tried everything but still couldn’t get a solution for it ,

so another method i tried was to to make sure it works fine, created a VPGs manually from web, got the skeleton of template used by that VPGSettingsIdentifier, so just to make sure i redeployed VPGs with different name and different vpgsettingsidentifier, even with a confirmed VPG template,

i get the same error,

can any one suggest me how can i overcome it

Thanks