If you sell to a customer in one currency and receive payment in another currency, you can apply the payment to the sales invoice.
You must specify to what extent you want to allow the application of entries in different currencies.
Open the 
Sales & Receivables
Setup window.
On the General tab, in the Appln. between Currencies field, select one of the following options:
|
None |
Application between currencies is not allowed. |
|
EMU |
Application between EMU currencies is allowed. |
|
All |
Application between all currencies is allowed. |
Close the window.
Allowing for Rounding Differences when Applying Customer Ledger Entries