Failed to initiate document generation. - Docusign

Hi all, 

I am setting up Docusign in Salesforce. Authorization and connection with Docusign were already established. 

Currently I have prepared Envelope Template and Gen Template. When I am trying to generate and Preview the merge field data on document. 

Document does not gets generated and attached snap error is thrown. 

Current my User is System Admin. It had access of all the fields, which I am using in Document.  

I cannot find any integration user in my salesforce org which is dedicated for the Docusign.

How can I resolve this issue.?