Topic
You are not an organization admin. Please contact your DocuSign Administrator error occurs when attempting to integrate the OAuth - Admin Consent authentication for DocuSign.

Instructions 
This error occurs as the DocuSign Admin User requirements for this type of Authentication have not been completed on the DocuSign Account. DocuSign has a new Admin section in the online account portal where Organization Admins can be specified. This is a different permission than the DS Admin Permission. Please see the documentation below:

Nintex Help: Troubleshoot DocuSign Integration
DocuSign Help: Add Users
 

Note:
Admin tools must be enabled/purchased by DocuSign in order to use DocuSign for the 'Oauth - Admin Consent' option. 
If Admin tools are not enabled/purchased for the linked DocuSign Account, the alternative option will be 'Oauth - Individual Consent' which will be available in the September Nintex DocGen release. 
Release Notes

Admin section in DocuSign: