How to add a gift card to Apple Wallet?

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.

1. Start by going to settings>general>reset>and reset all settings.
2. Turn off your device and turn it back on.
3. Force reboot your device (Force reboot device - Apple Support)
4. Sometimes if you sign out of your Apple ID and back in it resolves the problem.
5. Make sure you are using the latest iOS/macOS update.
6. Make sure that your date and time is correct under Settings > General > Date & Time.
7. Make sure that you are connected to a known-good network and are not connected to a VPN.
8. Make sure that push notifications are set up correctly: Use notifications on your iPhone, iPad, and iPod touch.
9. Make sure that your zip code is accurate under Settings > [your name] > Payment & Shipping.
10. Check your Apple ID region to make sure it is correct. If it is correct, you may need to select the same region again. (Change your Apple ID country or region - Apple Support)
11. Check the region on your device to ensure it is correct (Settings>general>language & region - set to your region). If it is correct, you may need to select the same region again.
12. A passcode is required to use the Wallet app. 
13. You need to be in a region that supports Apple Pay - Countries and regions that support Apple Pay - Apple Support
14. Your bank needs to support Apple Pay - Apple Pay participating banks - Apple Support
15. If none of these suggestions are able to resolve your issue you can go here for further assistance - If you can't add cards to Wallet for Apple Pay - Apple Support
16. Apple Pay support can be reached here - Apple Pay Customers