We are integrating Amazon Simple Pay onto our web site. We are 99% done with the integration, but we have run into a problem and need someone who has done Amazon Payments integration before and has solved similar problems.

Here is our problem: Amazon returns an "invalid signature" error when a customer clicks on the Amazon checkout button. However, when we try testing the same code using the Amazon Sandbox, it works great. In both transactions, we are using the exact same details.

The code consists of the Simple Pay button signed with version 2 SHA method, and the IPN script is used to log the sale. We have tested the script using a Business account, with Sandbox access active as well. The signature script handles many different items, and it did create valid signatures using the Sandbox account. FPS and EC2 services are active at the Business account.

Please bid on one (1) hour of labor for you to help us debug this problem. You need to have substantial experience integrating Amazon Payments onto a web site. Please include the word "Excel" in your bid comments so that I know you understand these requirements. If you can finish this job quickly and can start immediately, we will likely end bidding in a few hours and select you.