Thank you for your coordination.
In this case, I think KAMA JV can allow changing only Commercial Invoice for Advance Payment but the Proforma Invoice should not be changed because L/C as a bank guarantee and assuring that we will receive the payment for goods on time and the correct amount.
If the client cannot make payment on the PO, the Bank will be required to cover the full or remaining amount of the PO.
in the event of T/T, no guarantee for the payment when the client received the goods, we may not receive the payment at all or if we produced the goods and waiting for payment before delivering