How do I use the App on Android to spend in store?
You must have NFC enabled and switched on on your device.
Open the app and hold your phone to the card terminal to pay; the phone will usually beep or vibrate to confirm the transaction. Some phones may ask for your thumb / finger print for security to authorise the payment - this depends on your device.
One4all does not impose any limit on the amount you can tap for but some retailers may, so it is best to ask before purchasing.