Amazon Pay is an online payments processing service that is owned by Amazon. Launched in 2007, Amazon Pay uses the consumer base of Amazon.com and focuses on giving users the option to pay with their Amazon accounts on external merchant websites. As of January 2019 the service is available in Austria, Belgium, Cyprus, Germany, Denmark, Spain, France, Hungary, Luxembourg, Republic of Ireland, India, Italy, Japan, Netherlands, Portugal, Sweden, United Kingdom, United States.
Amazon Pay incorporates a variety of products for buyers and merchants to process online payments.
Amazon Pay provides the option to purchase goods and services from websites and mobile apps using the addresses and payment methods stored in the Amazon account, such as credit cards or a direct debit bank account.
Amazon Pay Express
Amazon Pay Express is a payments processing service for simple E-commerce use cases on websites. Built on Amazon Pay but without requiring a full E-commerce integration  it uses a Java button code generator to create a button that can be copied and pasted onto a website or added via WordPress Plug-in. It is best suited for merchants selling a small number of products and with a single item in each order, such as a digital download.
Amazon Pay has undergone many changes in its evolution to improve the online payments processing for Amazon customers on external websites. While Amazon Pay is the most recent product, it represents the culmination of previous trial and error products, and strategic acquisitions.
Checkout by Amazon (CBA)
CBA was an E-commerce solution that allowed web merchants to accept Amazon account information and use Amazon for payment processing. CBA could manage several aspects of the transaction including order processing, promotional discounts, shipping rates, sales tax calculation, and up-selling. Depending on the needs of the merchant, CBA could be integrated into the merchant’s systems with manual processing (through Seller Central) or through SOAP APIs or downloadable CSV files. CBA also claimed to reduce bad debt because of Amazon’s fraud detection capabilities. CBA was discontinued in the UK and Germany in 2016 and is set for discontinuation in the U.S. in April 2017.
Amazon Flexible Payments Service (FPS)
FPS was an Amazon Web Service that allowed the transfer of money between two entities using a technology built on single, multiple, and unlimited use payment tokens. Merchants managed their use of the service via API or solution providers and accessed the account through the merchant account on the Amazon Payments website. The service was launched as a limited beta in August 2007, and later in February 2009 was promoted to General Availability . FPS differed from CBA in that FPS did not handle additional capabilities associated with order processing such as promotions, tax, and shipping. FPS also provided the payments processing for the Amazon Web Services DevPay service (https://aws.amazon.com/blogs/aws/make-money-fast/) but was discontinued on June 1, 2015.
GoPago technology acquisition
Amazon in 2013 acquired GoPago’s technology (mPayment) and hired their engineering and product teams. Amazon was interested in the mobile payment business. GoPago’s app allows shoppers to order and pay for goods and services before they arrive at a business.
In September 22, 2010, Amazon published a security advisory  regarding a security flaw in its Amazon Payments SDKs. This flaw allows a malicious shopper to shop for free in web stores using those SDKs. Amazon mandated all web stores to upgrade to its new SDKs before Nov. 1, 2010. Amazon acknowledged security researcher Rui Wang for finding this bug. The detail of the flaw is documented in the paper “How to Shop for Free Online – Security Analysis of Cashier-as-a-Service Based Web Stores” by Rui Wang, Shuo Chen, XiaoFeng Wang, and Shaz Qadeer.
^ “Launched in 2007”. August 3, 2007. Archived from the original on January 21, 2013. Retrieved June 10, 2012.
^ “E-commerce integration”.
^ “WordPress Plug-In”.
^ “April 2017”.
^ “Amazon Bought GoPago’s Mobile Payment Tech And Product/Engineering Team, DoubleBeam Bought The POS Business”. TechCrunch.
^ “Amazon Payments Signature Version 2 Validation”. 2010-09-22.
^ Rui Wang; Shuo Chen; XiaoFeng Wang; Shaz Qadeer. “How to Shop for Free Online – Security Analysis of Cashier-as-a-Service Based Web Stores”.