The service they offer to customers is exactly the same as APTs,...

The service they offer to customers is exactly the same as APTs, 4 equal instalments and no interest or fees if they're all paid on time. I don't know what legal trickery APT and Sezzle use behind the scenes but to the user the core product is identical. Maybe APT just beat Sezzle to it and proactively engaged with regulators which may have earnt them some goodwill.

Also APT has overcome every single regulatory hurdle it's faced, and every time has managed to either get off scot-free or complied without fundamentally altering its business model. They've faced a full-blown senate inquiry in Australia, they're not going to let something as simple as license compliance bring them down.