In order to prevent a Redeemable from being applied to base items or modifiers with zero price ($0), you should add an "Item Total Amount" attribute in the Line Item Selector that contains the applicable menu item IDs. The "Item Total Amount" attribute should be set to the option "is more than equal to", with the amount as "0.01". This setup will exclude items that have $0 as their price from qualifying for the redeemable.
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