Mobile transactions are highly not recommended as a payment method. They are a scam.
Doesn't matter what company does it, they are all a scam.
The problem is this, when a buyer sends an SMS purchase, they are not billed right away, they are billed at the monthly billing from phone service provider.
So, technically, the company (ZayPay or whatever) has to wait until the buyer is officially billed before you get paid.
On top of that, lots of fees are applied for services to obtain those money. So, right off the bat, you can lose a large chunk of those incomes.
Why people use SMS payment options is beyond me.