In order to purchase (or, it seems, to redeem the codes) you need Ventura 13.4 or later, or Sonoma.
But you can use the applications in Monterey, once you have bought them.
In this circumstance, you need to have temporary access to a Mac running 13.4 or later - maybe a friend's or a family member's mac. Make sure to log in to the App Store with YOUR Apple id. Redeem the codes and then delete the applications from that mac. This will associate the purchase with your Apple id.
Back in your Monterey mac: open the App Store, click on your account at the Bottom left. Locate the purchased apps in the list. Click the Cloud icon next to each of them, and you will be allowed to download a version compatible with Monterey.