You can manage your payments on a bill partially or as a full payment or even scheduled payments in order to be paid later
New G Solution gives you the ability of managing customers payments : if the payments are related to a sale order you can add them directly on it or even schedule them , otherwise you can add a debit or credit memo for your customers in order to manage customers’ balances.
You can edit the invoice many times as the status is still draft , if you confirmed it you will not be able to edit it any more.