I cannot call using Skype with Xperia Z4 Tablet WiFi (Xperia Ear Duo)

You might experience that you cannot make a Skype call using your Xperia Z4 Tablet WiFi with Xperia Ear Duo.

Update your Xperia Z4 Tablet WiFi to Android version 6.x or 7.x. After updating your tablet, you should be able to make Skype calls.