原来要先改好汇率, 才能填参考凭证. 先填了参考凭证, 就不能改汇率了.
You can change the exchange rate filling its field before entering the PO reference.
Procedure:
1 - Fill the Basic Data screen, including the amount.
2 - Go to the Details screen
3 - Enter the exchange rate manually
4 - Press ENTER
5 - Enter the PO Reference