Amazon SP-API feeds API POST_PRODUCT_PRICING_DATA Failing To Update Price

I tried using the Amazon Feeds API to upload a feed and was successful in updating the quantity.

But what about the price? It failed.

Here is the xml I uploaded:

       <?xml version="1.0" encoding="UTF-8"?>
          <AmazonEnvelope>
            <Header>
              <DocumentVersion>1.02</DocumentVersion>
              <MerchantIdentifier>XXXXXXXXXXXX</MerchantIdentifier>
            </Header>
            <MessageType>Price</MessageType>
            <Message>
              <MessageID>1</MessageID>
              <Price>
                <SKU>XXXXXXXXXXX</SKU>
                <StandardPrice currency="USD">100.00</StandardPrice>
              </Price>
            </Message>
          </AmazonEnvelope>

After waiting, the price remained the same.

How can I update the price? Is the above XML not correct to make the price change?

Please can you show me an example that will update the price via the feed API?

The Message node needs to specify operation type.

 <Message> 
      <MessageID>1</MessageID>
      <OperationType>Update</OperationType>
      <Price>                 
            <SKU>1234567</SKU>
            <StandardPrice currency="USD">100.00</StandardPrice>
       </Price>
     </Message>

  Other possible values are Delete and PartialUpdate