There are two variables that will impact the barcode scanning success rate at the point of sale.
1. The type of scanner being used. Most handheld scanners work well, but flatbeds will not.
2. The type of phone screen. Not all phone screens are equal. For example, the same barcode may scan very easily from an iPhone screen, but may not scan from a Droid screen. It depends on the device.
Adjusting the brightness of you phone will also greatly help your barcode to scan. You can change this setting by doing the following:
Open the app > Menu > Settings > check the box 'Barcode Brightness'. This will use max brightness when viewing your card barcodes.
You can also make the barcode image larger so that it is easier to scan.
After clicking on a card to open it, click on the "+" to the left of the barcode to make the barcode full screen. This should help when scanning.
If your barcode still won't scan, you can show the cashier the barcode/membership ID number that they can enter in manually.