To clarify: for many projects I'll take an installment upfront, a second payment at a project milestone and then a final payment 30 days after completion. To date I've been supplying an invoice for the total amount, with follow up statements for each payment. If we take 'correct' to loosely mean "I'm not going to end up with a convoluted tax return at the end of the year", is this the 'correct' way, or should I be issuing a separate invoice for each payment?
Follow up questions: what is the proper format for handling these types of payments? Where do you specify the schedule of payments? In the original invoice?