Unable to submit feed OrderAcknowledgement to cancel the order

Hello,

I set feed type as _POST_ORDER_ACKNOWLEDGEMENT_DATA_ and used this feed content XML to submit feed based on these posts:

`

<?xml version="1.0" encoding="utf-8"?>
<AmazonEnvelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">
    <Header>
        <DocumentVersion>1.01</DocumentVersion>
        <MerchantIdentifier>AGI50H4XXXXXX</MerchantIdentifier>
    </Header>
    <MessageType>OrderAcknowledgement</MessageType>
    <Message>
        <MessageID>1</MessageID>
        <OrderAcknowledgement>
            <AmazonOrderID>114-0751562-XXXXXXX</AmazonOrderID>
            <StatusCode>Failure</StatusCode>
            <Item>
                <AmazonOrderItemCode>23140510XXXXXX</AmazonOrderItemCode>
                <CancelReason>GeneralAdjustment</CancelReason>
            </Item>
        </OrderAcknowledgement>
    </Message>
</AmazonEnvelope>

`

the order status is pending, and it always returns error message below:

The data you submitted is incomplete or invalid. For help fixing this, see http://sellercentral.amazon.com/gp/help/30721

I think I have passed all of the required XML elements? or what I have missed from this?