I tested it on 3 devices (laptop, tablet and smartphone) and on all devices I can not see the “start order” button and it is not possible to scroll down.
The only possibility is to zoom out. But I think it’s not the user experience the plugin wants to provide. Most users will be confused.
So the problem is not that the popup is not working, the problem is that the popup is not scrolable or on a wrong position as the “start order” button is invisibile on smaller screens.