How should a freelancer ask for extra money after finding out that the agreed charge won't be enough?

[Btaliat]

If I want to be honest, the freelancers have to bear the consequences. This is the main reason why freelancers should try all their means to know more about the tasks and know the right amount to charge. If you have agreed on a particular amount before finding it out, it may be on you and not really on the clients. But you can still write a polite message to request from the clients.