Questions about adding gift cards to the app.

[Canadian Harmony]

I usually pay for all my food and souvenirs with gift cards. I know that it is an option to use to pay with the app but I can’t figure out how to add that as a payment option.
Also, can it be used to pay for merch or does that need to be a real card?

 

[twincruisers]

Disney gift cards to apple wallet