Use EventSub to recieve notifications in real time
Eventsub, is a transport agnostic notification system, which currently only offers a webhook transport (so your server would need to be web accessable + a Real SSL Cert)
Heres a nodeJS example on how to setup the basics
https://github.com/BarryCarlyon/twitch_misc/tree/main/eventsub/handlers/nodejs
Alternatively you can repeat poll the Get Custom Reward Redemption API.
You’ll also need to use this to catch missed rewards between “server restarts” on your side
For both you’ll need to use the Update Redemption Status endpoint to mark redeems as processed.