Facebook-owned WhatsApp ended support for millions of iOS and Android devices over the weekend.
Smartphones using Android version 2.3.7 “Gingerbread” or older and iPhones running iOS 8 and older will no longer be able to use the service.
The move comes after the company banned all Windows Phone devices after 31 December 2019.
The company said it was ending support for legacy operating systems that are no longer updated or installed on new devices.
Users of some devices will be able to update their operating system to continue using WhatsApp.
Devices such as the iPhone 4/4S, the iPhone 5 and the iPhone 6 can be updated to iOS 9, according to Apple – although the update may slow down older phones.
Most Android phones released after 2011 should be able to a supported version of the OS.
WhatsApp said it made the move because older handsets aren’t powerful enough to support upcoming features.
“This was a tough decision for us to make, but the right one in order to give people better ways to keep in touch with friends, family, and loved ones using WhatsApp,” the company said in a statement.
On its website, WhatsApp warned that on older phones “some features might stop functioning at any time”.
The company recommended users to upgrade to the latest OS version available for their phone.
Earlier this month WhatsApp reached 5 billion downloads on Google Play, only the second non-Google app to achieve the milestone – with the first being Facebook.