The main iOS app (from my first link above, which says that it's only for the iPhone) or the one from my second link - or, indeed, a completely different app? It would clearly help Smurfchops to know.
I have got an app the same as giggsie. What it does is links the ipad to an iphone so it looks like whatsapp works on the ipad but its actually receiving stuff from the iphone. If the iphone is off, rundown or out of data then the app doesn't work. Similarly I can relay phone calls from my iphone to ipad but the ipad can't do phonecalls unless its linked to the iphone.