How to cancel ONE item using amazon mws order adjustment feed? - amazon-mws

Question

I've been trying to cancel single item from an amazon order using their order adjustment feed, but every time I submit request I get:
ERROR 18028: The data you submitted with this item is incomplete or invalid. Please resubmit the item with all required fields completed with valid data.
I've used this xml in my requests:
<?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>XXXXXXXXX</MerchantIdentifier>
</Header>
<MessageType>OrderAdjustment</MessageType>
<Message>
<MessageID>1</MessageID>
<OperationType>Update</OperationType>
<OrderAdjustment>
<AmazonOrderID>305-XXXXXXX-XXXXXXX</AmazonOrderID>
<ActionType>Cancel</ActionType>
<AdjustedItem>
<AmazonOrderItemCode>209XXXXXXXXXXX</AmazonOrderItemCode>
<AdjustmentReason>NoInventory</AdjustmentReason>
<QuantityCancelled>1</QuantityCancelled>
</AdjustedItem>
</OrderAdjustment>
</Message>
</AmazonEnvelope>
I have double checked my xml and it seems to be valid according to amazon's xsd schema.
I would appreciate if someone with similar problem could share their experience.

Answer 1

TLDR: Try setting the ActionType to Refund instead of Cancel.
This concerns merchant that do their own fulfillment.
Two scenarios come to mind, an order with:
two items, each with quantity 1
one item with quantity 2
Logically, a partial cancel involves fulfilling one item and canceling the second.
Since the MWS API does not have a single operation for a partial cancel, the application has to first fulfill the second item and then refund it.
That means first sending an OrderFulfillment message for the second item and then sending an OrderAdjustment for it.
I've found that the ActionType of Cancel gives the same error message as seen in the original post while a value of Refund is successfully processed.