The Pay button shows before you get to the payment section. I thought it was the next step, so I clicked it twice. Nothing happened. But when I scrolled down, I saw errors in red.
The pay button covers up half of the feedback question at the bottom (the one I clicked to submit this).
There is no submit button on this feedback form in mobile is cut off by the pay button as well you can't scroll this form), so this form cannot be submitted until after payment.
Lots of issues in mobile. Just try and you'll see.