Serious question: How does Circle afford a $400 million price tag when they've only raised $135 million? Their main product seems to be a Venmo clone, complete with the lack of fees. Surely, they're not making that much money selling user data.
So they're probably buying Polo for X shares of Circle, where X depends on their current undisclosed valuation. But it's probably a pretty big chunk of their total.
My guess is that equity in Circle was part of the purchase price -- hard to know for sure since the terms weren't announced, but this probably wasn't an all-cash deal.