Facebook is jumping in the mobile payments bandwagon, as the company users in the United States can now use its Pay service. Facebook Pay promises to offer users an easy and secure payment experience not only across Facebook but also via Messenger, Instagram, and WhatsApp.The new service allows Facebook users to add their preferred payment method to make payments and purchases on the apps mentioned above. Facebook Pay lets users set it up app-by-app, or choose to set it up for use across all apps, which means that it won't be automatically set up across the apps where the user is active ...