Niko Access Control - Digital - Why do I have to ‘check’ the QR code?

This is for security reasons. Once the 2-wire external video unit has been scanned and linked to an App account, the QR code is marked as having been used.
This avoids misuse by visitors who could scan the QR code on your screen, allowing them to open your door.
For families with several mobiles, you can simply log on with the same login ID. There is no need to scan the QR code to activate new mobiles.