What does "Refund owed" on an invoice mean?

It means the tenant paid toward their share of a bill that was later written off or voided. On the tenant's Payments tab Kera adds "You owe this tenant a refund of $… from a written-off bill. It isn't paid out or credited automatically." The balance sheet lists it as Owed to Tenants.

Kera doesn't pay out or apply this refund for you. Refund the tenant outside Kera; contact Kera support to clear the flag.