Bank by Emma Quigley

Financial literacy made fun.
An action-packed and funny story about the rise and fall of a bank set up by school friends.
This is the hilarious story of a group of friends who set up a bank to lend money to their schoolmates. They have no trouble finding customers and before long they are rolling in cash. When they are asked by a pair of supersmart techy sisters to invest in their dating app, it looks like they can't possibly lose, and soon everyone at school wants to deposit money with them as well.

The whole thing starts to unravel all too soon when the app breaks down; an investment involving performing piglets goes down the pan; and the local gangster family takes far too much interest in their doings.

As the bank comes crashing down and the money starts to melt away, the young bankers are desperate to rescue their emergency stash - only to find that one of their group has cleverly hidden it in a not-so-clever place.