Hmmm.  I was unable to zap mike@mikehardcastle.com, but looks like mhardcastle@getalby.com worked fine.  (I hope that's you 😉).

I'm using NWC with Cashu.me - which I believe is a very experimental wallet - so maybe that has something to do with it... I've been zapping plenty with it though for weeks now; and, this is the first issue I've run into... I've even been zapping from different clients.  So, who knows? 🤷