I have a customer who would like to pay in installments. Is it possible to provide one invoice so that the asking price is clearly stated, then continue the transaction until the payment is made in full before I ship?
Unfortunately with Website Payments Standard there are no built in features or options to support what you have in mind. One possible work around could be the use of a Subscription item button. They pay you X amount X times and then you ship the item.
Another option would be to use Website Payments Pro where as you you are in control of how you want to manage your transactions.
