1)
To be able to apply a receipt in one currency to one or more transactions in a different currency, set the system profile option AR: Enable Cross Currency to Yes.
You can define this profile option at the Site, Application, or User level.

2)
Also define Entered Currency Balancing account for your ledger.
When you create a cross currency receipt application, the resulting accounting entry consists of two currencies:
the entered currency and the functional currency.
The journal must be balanced in both currencies. Entered Currency Balancing account is used for this purpose.