Running invoice in Reckon Accounts Accounting Small Business Edition

If I have a project with a customer which requires part payments during the job, how is this best carried out in Accounts Accounting edition? Presently, I send out a running invoice made up in Excel and then give the client one invoice made from Reckon. My software is not setup for running invoices. I see the option for creating 'sales receipts', and wonder if this could be sent, and receipted against the main project invoice? Thank you for your input