Why can’t I add my gift card to the wallet app on my iPhone?
How to add my gift card to Apple Pay?
iPhone XS Max, iOS 14
Go to this link - Add and manage passes in Wallet on iPhone - Apple Support, please note that passes cannot be directly added within wallet, except for QR code enabled passes. For everything else, its done either through the associated app, an email, airdrop or a link in a website.