If your smartphone or tablet uses iOS 10 or Android 6 with Duo, then you need to upgrade to newer versions of the operating software by July 28. After that date, Duo will not work securely with iOS 10 or Android 6.
Duo Security announced the end of Duo support for iOS 10 and Android 6 on May 1. “Focusing on newer [operating systems] allows Duo to continue building helpful and secure features,” the company said. “We encourage users to upgrade to the latest OS versions to ensure devices are not vulnerable to security issues and to provide … the best Duo Mobile experience.”