This document describes the troubleshooting procedure when experiencing the NSURLErrorDomain -999 message in the Duo Mobile App.
The NSURLErrorDomain -999 message happens semi-frequently during Duo pushes. The error has only been reported on iOS devices. The error happens when there is a network error within the app during a push. A troubleshooting step to resolve the issue is to toggle wifi and use cellular data, or to switch to a different wifi network if available.
Duo's Documentation: https://help.duo.com/s/article/7566