The difference between the converted $NZ the customer has paid for an invoice, and the converted $NZ the customer was billed on that invoice, is 'Foreign Currency Realisation'. Due to exchange rate fluctuations, when the Customer Receipt transaction is processed, this exchange rate difference is processed into the "FX Realisation account".
Setting up an FX Realisation account:
The FX Realisation account is set up within the function General Ledger Account Maintenance <GLAM>. The procedure is as follows: