You can't add a gift card to mobile pay for quick service.
You can add it to google pay - so for shopping at stores, you can pull it up on your google pay and use it that way.
I wish I could just go to the register and pay for my food! Darn technology!
In the past, you could not use a Disney gift card with mobile order, but now you can. You just can't store the gift card number in the system. You have to enter the card number each time you use it.
The other thing to know when using a gift card is that you can't use TWO gift cards to pay for a 1 mobile order. So if your order is $50, but the gift card only has a balance of $45, the rest of the balance will go on the default credit card that is listed in the Mobile order system. I'm not 100% positive, but I think you have to give provide Mobile order with a cc to use the system. But then when you go to place an order- you can choose how you want to pay. You can choose to use the default card- OR - a different payment method - such as the gift card or a different credit card. (assuming the gift card balance is enough to pay for the whole order.)
If anyone plans to use a git card with mobile order, I suggest getting one big gift card, rather than multiple small ones. Small $25 gift cards aren't very useful when using mobile order. Suppose you order
one meal :$17 entrée combo+$4drink+plus tax.. You'd have $4 left over, and there's almost no WDW food that costs under $4. If you have 2 people, good luck ordering 2 WDW entrees for under $25.
If, on the other hand, you have a $200 gift card, you can keep using that one card for multiple orders.
One tip I like when using gift cards is to carry a mini-sharpie. Sharpie works well to write on the card the remaining balance, and/or an big X when the card is empty. In some cases, you have to keep the empty card, because items you return go back on that card.
The mini Sharpies are nice and small for WDW. Regular one would be fine too. The mini ones are sold at craft and hardware stores. Usually they are right next to the registers, where stores sell candy/batteries/impulse-buys.
Another simple way to keep track of the balance on a gift card while at WDW is simply to wrap the most recent receipt around the gift card. The remaining balance is print on it.