The Amazon Product Advertising API returns errors in three categories so that you can easily determine how best to handle the problem:

•  "2XX" errors are caused by mistakes in the request. For example, your request might be missing a required parameter. The error message in the response gives an indication what is wrong.
• "4XX" errors are non-transient errors. Upon receiving this error, resubmit the request.
• "5XX" errors are transient errors reflecting an error internal to Amazon. A 503 error means that you are submitting requests too quickly and your requests are being throttled. If this is the case, you need to slow your request rate to one request per second.
•  If this doesn’t help diagnose your error, you will want to check with the Getting Started Guide for more details about the issue. You can also check the Best Practices Guide for more suggestions.
• If no helpful information can be found there, please post your question to the Product Advertising API Forums. Many experienced members of the Amazon Associates program regularly participate in the forums, and often answer questions.