I had this at Sainsbury’s the other day.
My nectar card app needed my password. I didn’t know it. So had to reset it via the app, an email and a 6 digit code. All while everyone behind waited in the queue.
I was a £12 saving so I made them wait.
Good work
The more savings that are locked behind an app that frequently doesn't work, meaning you have to inconvenience the shops ability to sell things the better. Just make the 'barcode' part of the app permanent available wether you are signed in or not, or give us a physical card. I've taken a photo of mine now to scan of the app crashes.
And this happend to me when my Lidl app opened ok but didn't register at the till the other day so I missed out on a number of savings, the cashier didn't tell me it hadn't scanned even though it did beep an acknowledgement. I made her refund all the shopping, scan it again and scan the app again. All while a queue of 5 or 6 people awkwardly stood around waiting for an apology from me that was never going to come.