Seeking possible reasons for issues in ION API calls

Hi,

 

I am working on making Ming.le API calls in ION. I am trying to call 'Assign ION Task Item' API with my User GUID, AssignerID and AssigneeID is my User ID and I am getting below error(Fault 1025) though my user details are present in Social User Table:

 

 

Also, when I am trying to assign task to someone else, it says 'Unauthorized user. User GUID is empty or user does not have sufficient privileges to access APIs' (Fault 901) though that user has full access on that XI environment and those details are also present in Social User table.

 

 

Can you please let me know the possible reasons behind these issues?
I also want to know if there's any document or tutorial available to study detailed behavior of ION APIs and the kind of issues and their possible fixes.

 

Thank you in Advance.

 

Regards,

Ridhima Sinha