API

There is a custom event which will be called when someone gets a reward.

public class CustomRewardListener implements Listener {
  
  @EventHandler
  public void onReward(RewardEvent e) {
    //Do something
  }

}

You could cancel the event and use your own economy plugin for example.

e.setCancelled(true);
YourPlugin.addMoney(e.getPlayer(), e.getReward());