Payment Gateway is a software interface between a web-based shopping cart and a merchant account. It's an e-commerce application service provider service that authorizes payments for e-businesses, online retailers, bricks and clicks, or traditional brick and mortar.

For that in 2007, PayPal introduced an optional security key that adds an additional layer of protection when logging into PayPal or eBay accounts. A security Key is a may be just like a physical device that an authorized user of computer services is given to aid in authentication. A user account tied to a security key has a modified login process; once the user enters their normal login ID and password, they are prompted to press a button on the security key, and then enter the six-digit number generated by the key to complete the login process. This two-factor authentication (T-FA) prevents an account from being compromised by a malicious third party without access to the physical security key. If a user loses their security key, they can authenticate by providing their credit card or bank account number listed on their account