Exchange rate issue in CCO & SAP B1

Hi,

Our SAP system local currency is USD but CCO local currency is SGD. When we post the receipt in CCO then based on B1if integration Sap Business one Invoice was posted in SGD with Sap exchange rate but payments not posted with Sap exchange rate because it follows CCO exchange rate due this reason payment entry have huge difference in Realize exchange rate gain & loss ledger. if Invoice is posted with Sap exchange rate then payment also should be posted with Sap exchange rate otherwise payment entry always have huge difference in Realize exchange ledger.