Both Discord and Steam have magic QR code scans. I believe on iOS you get a confirmation prompt before those apps can shift over. But you do not need to scan anything to redeem a card, anyone who presents something for you to scan is clearly baiting you.
If you receive these kind of messages on Steam, Be aware that IT'S A SCAM!⚠️ So by all means DO NOT scan the code ⛔ And contact your friend on another Social That their steam account got compromised!