Background video not playing on mobile devices

I got a problem with a background video (integrated with code) that is not autoplaying on some mobile devices. For example: The video is playing on my iPhoneXs but not on my clients iPhone. So it’s working on some devices and on some not.

I have integrated the following script which I found in another post, however it has not solved the problem yet.

Here’s the read only link:

Anyone got a solution or same problem?

Thanks in advance!