BPM Worklist REST API Issue

Summary:

Hi,

We are using BPM rest API to retrieve task in our custom screen and when we clicked on any task, it opens task form(shown in screen shot below) in a popup-window. But when we take any action(approve, reject) . it throws an error saying "you do not have permission to access this information", despite throwing error , it performs the successful action in backend.

Question is : why is it throwing error, because user has access to take actions on these notifications

API details:

Has anyone faced such issue. please assist!!

NOTE: it works fine, when opening the same notification from BPM worklist directly and works fine with any action taken there.