By the end of the year, eBay's (EBAY 0.07%) PayPal will be accepted in more than 2 million retailers across the U.S., giving it a unique opportunity to enter the offline-payments business. But before PayPal can become the dominant player it hopes to be, there are a number of challenges it must address. In this video, Fool contributor Steve Heller discusses PayPal's most obvious challenge and how it should overcome it.