- Least amount of cognitive and physical effort for the cashier person
- big centered QR code
- audio and strong visual feedback for paid invoice
Discussion
that, plus reliability.
This is probably the most important and I would add:
fast finality. You must be sure within a few seconds (30s max) that the payment is either confirm or cancelled.
It happened to me twice that my boltcard didn't confirm the payment on the PoS until the 60s time out (way too long), then a new invoice was generated and paid with another waller (Phoenix, Breez, WoS...) then 10min later the inital invoice was paid.
This should never happen or at least there should be automatic refund.
