Not to worry about that one: that's the difference between what has been rewarded by Ocean and what has been actually paid out. So even if all zappool users disappear at once, those few sats will be paid out by Ocean in a few days. Now that Zappool is working quite stable, my task is to make some publicity and attract more users. I want to finish real ZAPs (not only LN payment, but Nostr-visible zap), and it is working already in my test environment, so I will turn it on soon!