Most of what sells on Amazon isn’t sold by Amazon. Independent sellers accounted for 61% of the units sold worldwide in the second quarter of 2026, according to Amazon’s quarterly results.
In the UK, around 100,000 small businesses sell on Amazon, and they make up more than half of all physical product sales in the UK store. UK sellers also exported over £3.8 billion through it in 2024.
Three ways to fulfill
Sellers choose how each order reaches the customer. With Fulfillment by Amazon (FBA), Amazon stores, packs and ships the stock. With merchant fulfillment, the seller does. Seller Fulfilled Prime sits between the two, shipping from your own UK warehouse while keeping the Prime badge.
For the EU stores, Pan-European FBA spreads stock across Amazon’s European network for sellers who list the same product in several countries.
Payouts arrive with Amazon’s fees and any refunds already taken off, and the settlement report breaks each one down. Through the API, the same financial events are available as they happen, without waiting for the settlement period to close.
The Selling Partner API
The Selling Partner API (SP-API) is Amazon’s REST API for sellers’ orders, shipments, payments and inventory. It replaced the older MWS, which Amazon switched off after March 31, 2024. Its sections cover orders, reports, feeds, listings, FBA inventory, finances and notifications.
A business can register a private app for its own use on a Professional selling account, while apps for other sellers go through Amazon’s Appstore. Customer details are protected by roles, and the ones that unlock personal data ask the developer to explain how it’s used and secured.
Limits and testing
Every operation has its own rate and burst limit, and some adjust automatically to each seller’s business needs. Submitting a listings feed, for example, allows about one request every two minutes, with bursts of up to 15.
There are two sandboxes for testing: a static one that returns fixed sample responses, and a dynamic one that answers realistically based on the request.
Notifications
Instead of asking repeatedly, an integration can subscribe to events such as an order changing status, a Buy Box change, FBA stock moving or a report finishing. Amazon suggests a regular check alongside them as a backup.
What’s new
A new version of the Orders API launched in January 2026, and the older order operations retire on March 27, 2027. Listings feeds moved to JSON in 2025, and the old settlement report formats are replaced by a new flat file version from November 11, 2026.
Amazon has also decided not to go ahead with the developer fees it had announced for the API.
One channel among six
Amazon is one of six channels in the order-level P&L we built for a UK retailer in health and beauty. Marketplace fees there carry a detail that rarely makes it into a spreadsheet: in several territories, a digital services tax is charged on top of the fee itself, and the engine takes both off each order.
The same retailer’s markdown engine grades products on revenue from every channel, so a product that sells well on Amazon and slowly on the website is graded on its total sales. Slow stock, unsold for 90 days, fell to 4.8% of stock value, from about 12%.