This error occurs when the StatusCode value you provide in your order acknowledgement feed is invalid. Valid values for StatusCode include the following:
The StatusCode value indicates whether you were able to successfully import an order (Success) or whether the could not be imported (Failure). When you specify a StatusCode of Failure for an order, Amazon will immediately cancel the order and refund the purchase amount to the customer. Do not supply of a StatusCode value of Failure when an order cannot be fulfilled due to inventory restrictions. In this case, you should submit an order adjustment feed instead with a valid AdjustmentReason.
To resolve this error, please resubmit your order acknowledgement feed with a valid StatusCode value.