Users of Amazon’s Product Advertising API will begin seeing the following error as of about November 1st:
Your request is missing required parameters. Required parameters include AssociateTag.
This is due to changing requirements to the Product Advertising API. The AssociateTag parameter is now a required and validated field. You can see in the list of changes that it is the first thing mentioned.
These changes are made to keep the Product Advertising API in line with its purpose of driving affiliate sales through the Amazon.com website. The AssociateTag is a tag generated from your Amazon Associates account.
So far, it looks like the tag is not entirely validated to your account. I’ve had luck using fictitious tags such as aztag-20.