You can
- Long Poll https://dev.twitch.tv/docs/api/reference#get-custom-reward-redemption
- Use EventSub https://dev.twitch.tv/docs/eventsub/eventsub-subscription-types#channelchannel_points_custom_reward_redemptionadd
- Use PubSub https://dev.twitch.tv/docs/pubsub#topics
EventSub is the “best” solution here.