in addition to the above answer - the supplier requires a payment before the delivery of services or goods (case of supplier who do not want to take financial risk with a brand new customer); in this case you only have to record a payment (no P/L account is concerned) evn if a pro-forma is received as a supporting document; when the sale is achieved (by the actual delivery of service or goods) an invoice is issued and thus recorded and it is already paid. - the sale/contract is such that some significant costs on the supplier's side are incurred well before the final service is achieved; in this situation it is a best practice for the parties to decide of several payment terms; the parties can decide to base payments on interim invoices; then a revenue must be accounted for (client side) and VAT must be included. - Costs and related revenues must be recorded in the same accounting period (accounting principle); at least within the same fiscal year.

Hi thanks for the answers, I understood how to do it for clients, it's a little weird what it does but it can work for my country's accontancy, just I wonder if it can make a recipt or voucher instead of a invoice for the advance.

For suppliers was a little more complex and still can't understand how to make advance payments in OERP, hope someone can explain it to me a little easier if I find something I'll post it

thanks