Apple Pay is now available at more than 2 million retail locations, Apple has confirmed. Additional merchants will also add support for the service soon, including Crate & Barrel, Chick-fil-A, and Au Bon Pain.

Apple confirmed the latest milestone to The Business Times, and added that in-app Apple Pay purchases more than doubled in the last six months of 2015. However, it's thought many iPhone users are still reluctant to use its mobile payments service.

Online retailer added Apple Pay support earlier this week after receiving requests from customers "for quite a while," said Aki Iida, head of mobile for Zappos, who insists that it will make the shopping experience easier.

However, Iida still sees Apple Pay as a challenge, and says "customers have to change their mindset" to view Apple Pay as "a feature they want to use." As of October, just 16.6 percent of people with a compatible iPhone had tried Apple Pay, according to one survey.

Despite the reservations, mobile payments continue to grow, and are expected to account for $620 billion in transactions throughout 2016. That's up from just $450 billion last year, according to the latest data from TrendForce.

Samsung will hope to play a big part in that with its own Apple Pay rival, Samsung Pay, which is compatible with traditional magnetic card readers and does not rely on NFC. It is therefore accepted almost anywhere.