Buyers pay with the cards and details already saved in their Amazon account — one of the highest-trust wallets in the US, Europe, UK and Japan. Registration is self-serve in Amazon Pay Seller Central, but travel and tour services are a restricted category that needs Amazon's prior approval before you can take payments (see pay.amazon.com/help/6023). You'll find the Merchant ID, Store ID and API keys under Seller Central → Integration Central.