So, two problems here. It's not "safe." It safely arrives at its destination, but for most people, a safe money transaction is one that's protected from fraud somehow, which this is not. And it's not "backed" by banks so much as it is backed by your bank account. Again, backed by banks sounds like fraud protection. I don't think there's anything wrong with Zelle. It sounds like a useful service. But unless they are sanguine about these kinds of problems occurring then they ought to make it very clear to not send Zelle to a destination you don't 100% trust. That the only guarantee here is for guaranteed delivery of your cash and nothing else. So that's not quite the same as mailing an envelope of cash, which I know from personal experience as a lad is inherently unsafe even if the destination is your best friend's house.