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3) Credit Note (Goods Return) / Credit Note (Invoice Correction) may be posted with or without ACP.
To use option to revert ACP as items are returned from customer, enable an option in Administration > Settings > Sales > Calculate Cost of Goods Sold in Credit Note:
As this option is enabled, Credit Note picks ACP from basic Invoice depending on the settings:
In case, if Credit Note has no basic, then ACP may be added manually at Inventory tab as Cost of Goods Sold:
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