I have had problems using SP, but it seems to me it's the cashier who is not tapping the right button. If I take the time to explain that I want to use SP and they need to get ready to use a physical credit card, they are amazed that SP works. I did get a "Card Read Error" at the self checkout at Smith's, but my stubbornness prevailed and after repeated attempts, SP was accepted. I once had to move to a different self-checkout at a Walmart because the Walmart employee kept nagging that it doesn't work and kept reaching over me to tap the screen. I finally went to a different till and did it quickly while she was voiding the stuff I scanned at the last till. Once the cashiers around town have seem me use SP, they know what to expect and everything goes smoothly. Now if I could just get the Subway employees trained so I can pay with the Subway app...