Can I just say “Stocard“? That’s a Google Play link – search the App Store and you’ll find it for iOS too…
This nifty little app does a very valuable thing – it gets rid of cards.
Press on any one of these and you get a large barcode which should work with most readers. It works in many countries so have a look and see how it is for you.
Many thanks to Qualipet for telling me about this when they sent my customer card!!!