I want to change unit price to lower price but prompt error message and not allowed to do that. ‘Cannot change price of promotion item. Please use row discount.’ Why is that?
Possible Reason :
The item had set in promotion maintenance and since that is promotion item so the system not allowed to edit the unit price.
If that item is intended as promotion item, you can further give discount by using row discount or total discount. Else just remove the item from promotion or inactive that promotion.
By: CK 20200323, Jacky 20200324 
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