WhatsApp for Windows Phone is one of the few apps on Windows 10 Mobile today that continues to receive frequent updates from its developer. Unfortunately, the app itself is one based on Silverlight, which is what apps built for Windows Phone 8.1 used back in 2014. This means the app isn't a Universal Windows Platform app (UWP,) and as such doesn't run across all the different Windows 10 platforms and devices available today.