Unable to authorize: Unknown authentication error

Issue

The following error occurs when trying to authorize the Nintex DocGen for Salesforce app on the Admin tab:

Unable to authorize: Unknown authentication error. Error id:

Resolution

1. Verify if the Salesforce environment is up to date with Remote Site Setting, IP Address Whitelisting, and CSP Trust Sites. For more information, see Documentation for Settings.

2. Verify if your users are using Profile Based Login IP Ranges. If so, you will need to add our IP Addresses on the Profile Level.