Apple requires that users approve certain functions for specific apps, such as the camera. If your driver sees a grey screen when attempting to scan a barcode, the Gimme App was most likely denied permission to access the iPad's camera.
The first time a user attempts to scan a barcode using Gimme, they'll be prompted with the following message:
If a user selects "Don't Allow", Gimme will not be able to use the iPad's camera within the App.
1. Navigate to "Settings" from the iPad's home screen.
2. On the left panel, scroll down and tap "Gimme".
3. Edit Gimme's permissions to enable the camera and ensure App permissions match those in the example below.
If the issue persists, please see Apple's Guide for iPad camera troubleshooting.