Google Ads has added two additional promo code options under the promotion details section of promotions assets. Instead of there being a way to enter a promo code, you can now also offer bar code or QR code methods for promotion codes in your ads.
Thomas Eccel spotted this and posted about it on LinkedIn, he posted a screenshot and shared some of the help documentation in his post.
Here is the screenshot:
You need to enter your Barcode Number and select your Barcode in Aztec, Data Matrix, EAN-8, etc.
For QR code, you can directly encode your text with one limitation of max 720 characters and no links.
Forum discussion at LinkedIn.