All responses contain an IsValid element, for example:

<IsValid>False</IsValid>

The IsValid element tells you whether or not there is an error in the syntax of any elements of the request and if all required parameters are included.. For example, if you were to omit the Operation parameter, which is required in every request, Product Advertising API would set IsValid to False and not process your request. Typically, these kinds of errors are a little more subtle. Typical errors are incorrectly capitalized parameters or values, or the failure to include a required parameter in the request. For example, in the following request, the SearchIndex parameter is entered as "Searchindex."

http://ecs.amazonaws.com/onca/xml?
Service=AWSECommerceService&
AWSAccessKeyId=[AWS Access Key ID]&
Operation=ItemSearch&
Keywords=Potter&
Searchindex=Books

Product Advertising API returns the following error:

<Errors>
  <Error>
    <Code>AWS.MissingParameters</Code> 
    <Message>Your request is missing required parameters. Required parameters include SearchIndex.
    </Message> 
  </Error>
</Errors>

Product Advertising API believes that the request is missing the SearchIndex parameter just because the "I" was not capitalized in the parameter name.

In the sample response, notice that the error consists of an error code that identifies the error, and an error message that describes the error. The error messages is in the language of the locale.

For a detailed list of error codes and messages, see Error Codes and Messages section of the API Reference.