An Apple iphone 6 with Apple Pay is shown in this photo illustration in Encinitas , California June 3, 2015 More than 18 months after Apple Pay took the United States by storm, the smartphone giant has made only a small dent in the global payments market, snagged by technical challenges, low consumer take-up and resistance from banks. The service is available in six countries and among a limited range of banks, though in recent weeks Apple has added four banks to its sole Singapore partner American Express; Australia and New Zealand Banking Group in Australia; and Canada's five big banks. Apple Pay usage totalled $10.9 billion last year, the vast majority of that in the United States. That is less than the annual volume of transactions in Kenya, a mobile payments pioneer, according to research firm Timetric. And its global turnover is a drop in the bucket in China, where Internet giants Alibaba and Tencent dominate the world's biggest mobile payments market - with a...