How to do advance payment against PO for this is there any T.code

Hello,

Lt's say for ex: Once Po is created how to pay the advance payment against PO to the vendor, for that is there any transaction code.

Once advance payment is made against PO, again system should not allow for ammendement

So like this to control the system what are the configuration settings need to be done please explain

Early action in this matter will be highly appreciated.