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 a clear indication what is wrong.

4XX errors are transient errors. These errors don’t indicate there’s anything wrong with Product Advertising API. So, upon receiving this error, resubmit the request.

5XX errors are non-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.