Paydiant Inc., a Wellesley firm developing back-end technology for retailers and banks to create their own mobile commerce and payment apps, said Tuesday that it has closed a $12 million round of Series B financing.

The round was led by Stage 1 Ventures. The Series B round also included existing investors North Bridge Venture Partners and General Catalyst Partners. Paydiant said it raised $7.6 million in early 2011.

According to Paydiant, other mobile payments systems require consumers to buy new phones or retailers to invest in costly new payment terminals, but Paydiant claims that its technology works with existing smartphones, point-of-sale systems, and payment terminals, including entry-level devices.