From FI side there is f-47 and f-48 tcodes for downpayment. In f-48 yhere is an entry for purchasing doc where PO number can be entered. But, big issue is this process in FI side will go through lot of transactions and processes as first this down payment must be moved from spl.ledger to leading ledger and then it must be cleared. This is more easily done directly on MM side. SAP had done much better standard process by business function "LOG_MMFI_P2P”. Once, this business function is activated in SFW5 the there will an tab" periodic processing" added in ME21n in PO header level. Also, field called as "DP Category" will be added in line item level. You can specify one line item in po as down payment while keeping other items under normal p2p process. DP Category or Down Payment Category in PO line item level will require addition data. There are two types of dp categories, mandatory dp means this dp is mandatory for this po now; or voluntary dp which means company is paying vendor voluntarily. This dp categories have no effect in the end, it is just for reporting purpose. Then enter down payment amount and down payment percentage. Now, system will not allow to save the po unless due-date is specified under 'invoice' tab of line item. This is the reason why, I think SAP had done a good job by adding this complex FI functionality to PO config directly. Once, due date is entered you must be able to save the po. Now, fi teams can directly control the dp payment using tcode ME2DP. Or using ME2DP, select the po and its line item to create down payment open line item to vendor. In the same PO, there can be another line item for which MIGO and MIRO are done to calcel off this down payment open item. :)