Amazon MWS API: - _POST_PRODUCT_DATA_ SubmitFeed gives error

I am trying to submit a new product feed for the the Beauty / HairCareProduct product.

Here is the xml request I am trying to submit.

    <?xml version="1.0" encoding="iso-8859-1"?>
    <AmazonEnvelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">
    <Header>
        <DocumentVersion>1.01</DocumentVersion>
        <MerchantIdentifier>xxxxxxxx</MerchantIdentifier>
      </Header>
      <MessageType>Product</MessageType>
      <PurgeAndReplace>false</PurgeAndReplace>
      <Message>
        <MessageID>1</MessageID>
        <OperationType>Update</OperationType>
        <Product>
            <SKU>BU07612251AC</SKU>
            <Condition>
                <ConditionType>New</ConditionType>
            </Condition>
            <DescriptionData>
                <Title>Coconut Oil Baobab Sulfate-Free Invigorating Shampoo</Title>
                <Brand>ORS</Brand>
                <Description>Lather-rich, sulfate-free shampoo gently cleanses while reparative oils and plant-derived protein nourish and help reinforce strands to invigorate and revive damaged hair and dry scalp</Description>
            </DescriptionData>
            <ProductData>
                <Beauty>
                    <ProductType>
                        <HairCareProduct>
                            <Directions>The product is applied on wet hair and massage into lather. Rinse well. ‭Repeat, if necessary, leaving on hair 2 to 3 minutes. Rinse thoroughly. ‭Follow with HAIRepair Restoring Conditioner. </Directions>
                        </HairCareProduct>
                    </ProductType>
                </Beauty>
            </ProductData>
        </Product>
    </Message>
</AmazonEnvelope>

When I submit this request and check the result, I can see the error as follows.

<?xml version="1.0" encoding="UTF-8"?>
<AmazonEnvelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">
    <Header>
        <DocumentVersion>1.02</DocumentVersion>
        <MerchantIdentifier>xxxxxxxxxx</MerchantIdentifier>
    </Header>
    <MessageType>ProcessingReport</MessageType>
    <Message>
        <MessageID>1</MessageID>
        <ProcessingReport>
            <DocumentTransactionID>xxxxxxx</DocumentTransactionID>
            <StatusCode>Complete</StatusCode>
            <ProcessingSummary>
                <MessagesProcessed>1</MessagesProcessed>
                <MessagesSuccessful>0</MessagesSuccessful>
                <MessagesWithError>2</MessagesWithError>
                <MessagesWithWarning>0</MessagesWithWarning>
            </ProcessingSummary>
            <Result>
                <MessageID>0</MessageID>
                <ResultCode>Error</ResultCode>
                <ResultMessageCode>90215</ResultMessageCode>
                <ResultDescription>100% of the products in your file did not process successfully. We recommend using Check My File to help you identify and correct common listing errors before updating your inventory. To use Check My File, upload your file on the "Add Products via Upload" page in the "Check My File" section.</ResultDescription>
            </Result>
            <Result>
                <MessageID>1</MessageID>
                <ResultCode>Error</ResultCode>
                <ResultMessageCode>99001</ResultMessageCode>
                <ResultDescription>A value is required for the "part_number" field.</ResultDescription>
                <AdditionalInfo>
                    <SKU>BU07612251AC</SKU>
                </AdditionalInfo>
            </Result>
        </ProcessingReport>
    </Message>
</AmazonEnvelope>

Please not, my category of product is Beauty / Haircare product. Let me know what's wrong in in xml file. I have tried lots of tutorials, examples to solve this, but no luck.