Async payments require mint support to be in place, apart from Minibits own test mint they should work on other Cashu dev kit based mints as well.

Free protocols get better over time! 🚀 #cashu now supports asynchronous handling of Lightning payments. What does it mean? More reliable payments, of course. Timeouts, sats that seem lost in the void, and unnecessary recoveries should become a thing of the past. And Minibits wallet is first in line — async payments are now live via the latest over-the-air update, with experimental support by the Minibits mint!

Yes. Error means that the ecash notes sent to the mint were created using old, already used recovery indexes. Could be for previous incomplete rec9very attempt or other reason. The wallet tries to auto-heal such error normally. Try another send / lightning tx to see if it reappears. If so, head to Settings > Recovery and press "Increase indexes". Wallet should have return the reserved ecash back to spendable on error.