The WSDL for a given version of the License Service can be found at a URL that corresponds to the API version. For example, the current WSDL for the 2008-04-28 version of the License Service can be found here:
The WSDL includes the description of the request and response messages.
The previous and only other version of the License Service is 2007-06-05. For information about what changed with the 2008-04-28 release, see the Amazon DevPay release notes.