Issue
When running a Document Package with a SignNow delivery option, an error of "An error has occurred authenticating with SignNow. Confirm that your SignNow domain is configured to be used with Nintex Drawloop." occurs.
Resolution
Confirm their SignNow Configuration is setup correctly.
Reach out to SignNow as there is a feature they will need to activate.
Additional Information
Try sending directly through SignNow in Salesforce. If you can't do it there, then the functionality won't work with Drawloop.