Can I have my Gift Card on several devices?
You can only have your Gift Cards shared on several devices as long as Apple Wallet or Google Wallet apps are synched between those devices due to using the same Apple ID or Google ID. Meaning, if you digitise your card in one device, then you add it to your phone's wallet and your wallet is synched with your other devices, then you will see your card there as well.
Keep in mind that Gift Cards can only be digitised once in one device via the Giftify App, but they can be removed from your phone's wallet and added again from the Giftify app as many times as you want. Even if you uninstall the app, your active calls will remain in the app after installing it again.