Amazon FPS gives you the option of refunding an unused portion of a recurring payment that the
sender paid for but will not use. This might happen if, for example, the sender pays membership
fees twice annually but must cancel only three months into the membership. The
Refund action has an optional parameter, RefundAmount,
which enables you to refund all or only a portion of the transaction amount a sender paid.
The Amazon Payments web site, payments.amazon.com, enables senders to refund transactions from their user account. To provide transaction refunding functionality on your web site, use the following procedure.
To refund a transaction
Enable the sender to find the transaction to refund.
Obtain from that transaction either the TransactionId or the
CallerReference.
Submit a Refund request using one of those values.
For more information about this action, see Refund.
The following Refund request refunds the transaction specified by the
CallerReference and TransactionId.
https://fps.amazonaws.com/? Action=Refund& AWSAccessKeyId=0656Example83G2& SignatureVersion=1& Timestamp=2007-08-06T13%3A00%3A01Z& CallerReference=354897217& TransactionId=254656Example83987& Version=2008-09-17& Signature=<URL-encoded signature value>