ANZ Black bonus SC promotion

[flydoc]

Maybe an ambitious question, but...I was recently approved for this card which currently comes with 75 bonus QF SCs if you book and travel on a new QF return flight before 31/1/18. Does payment for the flight need to be made with the card? (this isn't explicit in the T&Cs). And has anyone had DSCs + 75 successfully credit after booking with a previously-purchased gift voucher from DSC promo, with the balance of the fare paid using the card? TIA