I like the idea, but even with a one-time code, the post office has a record of the reference number which could be linked back to the transaction. Along with

I like the idea, but even with a one-time code, the post office has a record of the reference number which could be linked back to the transaction. Along with some form of digital cash analogue (i'm not sure existing crypto is it), we'd be getting close to restoring some privacy in online transactions.