WhatsApp is planning to end support for Windows Phone. This goes for some older versions of Android and iOS as well. This means that by 31st December 2019, the chat app will stop working for Windows Phone and by next year, the Facebook owned app will no longer support smartphones powered by older iOS and Android versions according to official WhatsApp communication.
Smartphones running Android version 2.3.7 and iOS 7 will no longer be compatible with WhatsApp by February 1, 2020. This means that some WhatsApp features will stop working as the D day approaches. This includes creating new accounts or reverifying existing accounts.
It is imperative to switch to a device running the latest versions of either operating systems if you want to continue chatting with friends and family on WhatsApp.