Create a QR Code that will have a special behaviour when scanned for the first time. After that default URL will be displayed.
Login into your free account, create a coupon, set the number of vouchers for the coupon, download the vouchers, test a voucher and get redeeming statistics.
You can use one-time scannable QR Codes to create 1-time redeemable vouchers or create a QR Code to redirect the user to another URL after first scan.
Login into your account, create a QR Code and select One time from the available QR Code types then enter the two URLs for first and subsequent scans.
Create a one-time redeemable coupon with unique vouchers. Then merge them with your contact list in Mailchimp to include the vouchers in your campaign.