WhatsApp does not work on the older version of Android and iOS phones since February 2020.
WhatsApp is currently supported on phones running Android 4.0.3 and above and iOS 9 and above. It also supports phones running KaiOS 2.5.1 and above, available on the JioPhone and JioPhone 2. Users are hereby advised to check their phones for the updated OS versions to have uninterrupted access to the app.
It is the latest in a series of moves after the messaging app withdrew support for numerous devices in 2016, and then from all Windows phones on December 31, 2019.