21st Century Potty Reward

I’m late to the potty training game for many reasons, but one thing I’ve found is that motivating a two-year old can be different from a four-year-old. So how do you motivate a four-year-old to change from pooping in a pullup to something scary like a toilet that she barely likes to be on for 2 seconds to pee? She loves to shop, especially in the app store (I forgot to turn it off) so I offered to buy her a Toca Boca app for the iPad every time she succeeds in putting in a ‘big poop.’
At two bucks a piece it’s cheaper than the pullups habit, and it also has the bonus of keeping her dryer while avoiding using sugar as a reward. So far it’s working, although sometimes she’s upset that she can’t go when she wants to buy an app. Overall we’re getting there, and I’m hoping to leave the paper behind in the next few months!