Advanced one-time payment options
Advanced one-time payment options are only available for US and EU merchants by invite-only.
Charging more than the original order amount
If your business does not allow you to calculate the total order amount upfront, you might need to charge the buyer more than the original order amount. For example, your business might offer variable shipping, add-ons, or services that can incur additional costs after the buyer has placed their order.
You can request flexibility to charge the buyer more than the original order amount by setting the Checkout Session paymentDetails.allowOvercharge parameter to true. Note that you can only set this parameter during Checkout Session creation, either as part of Create Checkout Session or button checkoutSessionConfig parameter.
If you request allowOvercharge, Amazon Pay will automatically adjust the Charge Permission amountLimit to either 900% of the order amount or 500 USD/GBP/EUR and 70000 JPY (whichever is more). You will be able to request payment up to the amountLimit either using a single transaction or multiple transactions. Note that the higher amountLimit does not guarantee success and payment can still be declined (for example if the buyer has insufficient funds). To maximize the probability of success, we recommend that you process the charges asynchronously. See manage asychronous transactions for more info.
Extending order expiration date
A one-time Charge Permission expires 180 days after confirmation. You can extend this value to 13 months by setting Checkout Session paymentDetails.extendExpiration to true. Note that you can only set this parameter during Checkout Session creation, either as part of Create Checkout Session or button checkoutSessionConfig parameter.