Iphone 14: A friend's Device will not install apps

Hello,
Two friends of mine bought two Iphone 14’s together, from the same vendor, at the same time.
They are newbies, so had the devices configured by the same person at the same Apple Store.
One behaves as expected when installing apps.
The other one, instead, prompts my friend to tap twice to install, or confirm via the side button.
In either case, nothing happens, and the device returns to the previous screen on the App Store.
We tried with and without wi-fi, and by searching on the App Store direct, or via a link I shared.
No joy.
What could cause this bizarre behaviour?
Thanks for any ideas and suggestions anyone might provide.
Cheers,
Ollie

Hi, after pressing the side button it should say “processing payment”. Then it shoul ask for either a password or a face id. You need to press the butto fast though.

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