At the end of March the cell phones with operating system iOS 9 or earlier versions, Android 4.04 or earlier, and editions prior to KaiOS 2.4 will no longer be compatible with WhatsApp. This is due to a system update that the messaging service does every year.
Like other technology companies, every year we identify which are the most outdated devices and software and those with fewer users to decide what we stop supporting. It is also possible that those devices do not have the most recent security updates or the functionality required to run WhatsApp, ”explained in the official blog of the service.