Successful how? If you look at the worldwide scale, not by far. If you look at the US, again, the same answer.
Apple does not even make a significant blip on the world radar for a successful mobile payment app.
Sure, it is operating in quite a few markets, but there are other mobile payment apps that are much more successful if you look at the percentage of users using it (bKash, mPesa, Tigo, Paytm, EasyPaisa, etc.) than Apple itself.
If you look at it from a GDP perspective, then Kenya’s mPesa would be at the top with 42% of the country’s GD riding with one company, Safaricom. Now that is successful.
In the US, Starbucks mobile app for paying, Venmo and Square Cash are much more successful than Apple Pay.