It turns out that the 'Card Payment' Button does not appear on the iPhone when using Kashflow in the browser.
I was at a customers house the other day who wanted to pay by credit card while I was there. It turns out that the 'take payment' button DOES NOT appear on the site when used on the iPhone (6)? It does however when using the iPad. This seems a silly thing to do, as it was only lucky that I had my iPad with me. There should be a 'take payment' button on iPhone.