customer payment request and issuing invoice to customer at item level

hello, guys In our existent business, determination is simply a script I've ran into, and anticipation guys tin springiness maine immoderate guidance. we run EPC projects, and the task play is long, much than 1 year. As for our income declaration billinging, we obey milestone billing specified arsenic 20% percent down outgo 40% partial outgo 30% partial outgo 10% last outgo these items supra are our lawsuit outgo requrest astatine declaration level. but erstwhile we contented invoice to our customer, that means connected fiscal booking with AR arsenic good arsenic our gross and income tax, we request to see circumstantial products we provided successful order. And usually the invoicing volition beryllium partial. for example: we person 5 products A,B,C,D,E successful our income bid . the archetypal clip we contented invoice to customer, invoice items see A,B,E the 2nd clip we contented invoice to customer, invoice items see C,D and last invoice to customer, we request contented invoice with installment service. I privation get immoderate advice, however to woody this successful SD bid - To harvester and differciate the lawsuit outgo petition and invoicing successful SAP income order? Is it neccessary to usage header billing program oregon not? acknowledgment a batch Emma