Just saw your reply now; thanks.
So, it seems that one can get the credit via Delta charges such as drinks on flights, baggage fees, etc.,
or else by buying a Delta e-cert...but not by making purchases (cups, cookies, etc.) on deltashop.com, correct?

Also, the terms state, in part: "eGifts and Cards may only be used for the total purchase price of air transportation,
including taxes, fees, and surcharges imposed on the air transportation."

I wonder if you could pay the taxes on an award flight with an e-cert.
Has anyone done this?