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The PkId is the Primary Unique Identifier for the row in the database so this should not be changed or deleted and do not copy this when duplicating the row to create a new item. It must be blank when Operation = A and contain the exported value for Operation = D
The Operation should be Blank, A(Add item) or D(Set item Inactive).
Before the import can be done it's good to have all all referenced data such as Materials, Material Types, Price Grids, Cost Grids, Discount Grids imported. For details on importing this data refer to Inventory Settings
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