QR scanning code not working in Safari browser

I want a mobile page to scan QR-codes and display it's content. This is the page: https://ndvibes.com/demo/TicketSystem/check (index.html)

Very weird, it's working on Firefox (Linux), but not in Safari (iOS 11.4 /iPhone 6).

I thought the library I used didn't supported Safari, or Safari restricted it because of security reasons, but the demo of the library is working just fine on iPhone!

So it Safari seems to be supported, and it doesn't block it, because it's working in the demo...

I have no clue on how to fix this. Safari asks for permission to access the camera, when granted, it just does not display the camera-content. I also checked the settings of Safari, but didn't saw anything disabled that could block the webcam-video to show.

Edit: This code doesn't seem to work on Android either, very weird, the demo is working on desktop and mobile, and my own code is working on desktop, but doesn't work on mobile...

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