How do I add a database for my game, it has a bank and members add money but after certain amount (2 bil) it stops or freezes and you can't add anymore as in it says money deposited, it subtracts the amount, but after that bank wont show no more amount or add it.
Nowhere does my php code show it being limited either, so Im guessing it's the db.
My database for the bank looks like this:

id bank
type = int
length/values =15
not null
default

Does anyone know why it being limited from looking at this ?