For the what3words app
The minimum platform versions we support for new app versions are Android Marshmallow (6.0) and iOS 11.
If your device is incompatible with the versions above, you won’t be able to use the app, but you can still access what3words via what3words.com on your web browser.
Accessing the online map at what3words.com
Supported browsers for Android:
Chrome WebView on the current and previous major version of Android
Current version of Chrome for Android
Supported browsers for iOS:
Mobile Safari on the current and previous major version of iOS
Current version of Chrome for iOS