Please make sure that the V4S Mobile application is upgraded to version 1.34 or above from Salesforce App Exchange. And the V4S Kiosk application is upgraded to version 3.6.5 - 200012 or above on the iOS or on Android devices.
Once the apps are upgraded to the above-said versions, you see the Scan Members tab in the V4S Kiosk app. Upon clicking the Scan Members tab, you see the scanner option to scan the Contact QR code. Once you scan the Contact QR code, the contact is Checked-In. Use the same scan members screen to Check-Out the contact.
On some devices, the scanner does not open immediately when you go to the Scan members screen. Please go to any other tab in the Kiosk app or minimize the Kiosk app and then open the Kiosk app to see the scanner option.
To scan the contact QR code, please hold the QR code from the email or from the ID card in front of the scanner and move it immediately once you hear the beep. Or else, it will ask for check out and you see a message as "Sorry need to be logged in at least for 2 minutes".