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Q. How to drop DiscountPriceInfo container in revising call?
A. In revise request, if you set the StartPrice higher than the OriginalRetailPrice or MinimumAdvertisedPrice. The item will be a regular item and the DiscountPriceInfo container will be dropped from your item in question.
Q. Why I am getting warning 21919002 (Discounted pricing will not be applied to this item) for my AddFixedPriceItem call
A. If you want the item to have MAP treatment, then StartPrice should be less than OriginalRetailPrice or MinimumAdvertisedPrice.
Q. Can I add DiscountPriceInfo to listings that already exist using ReviseInventoryStatus API call?
A. No, you can't because DiscountPriceInfoType is only supported in AddItem family of calls