It was impossible last I had checked, but looking now I guess they enabled it on iPhone some time in 2020? But it required enabling push notifications? I’ve always added items to my cart, then finished the purchase on desktop to use smile.
I can’t currently find anything about it in the app. Either it has already been removed or its very difficult to find.
But likewise, in a couple of years I've only generated about ten dollars worth and I make at least a couple of purchases a week.
0.5% of net just isn't very much on low priced items.