Ann: Media Release, page-51

Banks make money by buying short term loans (your savings deposit) and selling long term loans (car loans, mortgages etc). The steeper the yield curve the better environment for the banks.

What's innovative here are
1) APT can make more money (bottom line) by improving the Pay-in-4 margin (they don't sell long term products). The improvement in margin comes from lower funding cost + lower credit risk + less transaction cost.
2) driving more engagement with customers as they want to own a large part of your waking life. APT is effectively a giant influencer which is the most lucrative part of the business. It's a classic playbook employed by Silicon Valley global tech firms.
3) It unlocks a range of revenue streams (top line) that previously wouldn't be possible (at least very hard to do).

All of these are done without the customers paying a cent to APT (late fee will become irrelevant once Money is adopted widely).