What happens when Paypal payment isn't instant?

Hi there, I just wanted to verify what is supposed to happen when a customer makes a purchase using Paypal, but their purchase isn't instant (meaning, for example, it will take 3-5 days for a bank transfer to happen). I would assume that a product key would *not* be generated automatically in that case, correct? But what happens when the transfer is complete? How do they get their key eventually?

Eric