To enable this functionality, the CRM account must be set to Allow Fulfillment Item EditsProduct Updates.
This can be set by going to CRM | Account and enabling the setting in the Company Information Additional Options section.
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Once this has been enabled, when an order has been placed for a product which is Marked Shippable on the campaign and is fulfilled to a valid fulfillment house, a new option Edit will display on the Fulfillment actions menu on the customer’s order:
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