Issue
When attempting to access the Nintex Forms for Office 365 app, the app errors with the message: "User access token redemption failed for site https://SiteURL/ using app with host name formso365.nintex.com 400 (BadRequest) response received from OAuth endpoint."
Error Code
User access token redemption failed for site https://SiteURL/ using app with host name formso365.nintex.com 400 (BadRequest) response received from OAuth endpoint.
Resolution
White-list *.nintex.com within the firewall that does 'Man in the Middle' encryption/decryption for the corporate network.
Additional Information
This can also result in the Nintex Workflow for Office 365 app hanging on "Connecting to Site."