Double check your invoice/receipt? - You should not have been charged GST on the gift card. I sell gift cards in my company, and no GST is chargeable on gift cards themselves. GST is charged at the time of purchasing the items that you pay for your gift cards. The gift cards are, in effect, cash. If you had a 19.99 gift card for Zwift, eg, you’d have $19.99 to redeem. The monthly cost is AUD$19.99 PLUS GST - so the cost is AUD21.99. Your card is $2 short - hence the extras.