Was the card officially sold in the country you are located? For example, if you purchase the card in the USA you can't use it in the Canadian store, only the USA store.
- Reset the iOS device. Nothing will be lost
Reset iOS device: Hold down the On/Off button and the Home button at the same time for at
least ten seconds, until the Apple logo appears.
- Go to Settings>iTunes and App Stores and sign out and sign back in
- Try redeeming on a computer
- Reset all settings
Go to Settings > General > Reset and tap Reset All Settings.
All your preferences and settings are reset. Information (such as contacts and calendars) and media (such as songs and videos) aren’t affected.
- Restore from backup. See:
- Restore to factory settings/new iOS device.