It took me a while to realize this isn't a falling sand (Powder Toy) type game. The phone has to lay flat, i.e. with the screen facing up.

It helps, if you lock orientation on the phone.

Whenever the phone detects an orientation change, it resets the layout.

Because if you turn it upside down, the sand pours out. Think of it as if you have sand in a rectangular tray with no lid.

It also responds to touch, which I didn't know until the third time I played with it.

Works for me in Safari — iPhone 17 Pro, all up to date

Do you have shake as undo still enabled? It's one of the most annoying features in iOS.

The sand is pouring onto the phone screen so if your phone is tilted or upside down it looks illogical