Recording a foreign currency invoice is similar to recording an invoice in your base or local currency.
Before you record a foreign currency invoice, ensure that
Enter a suitable exchange rate here, as Zoho Invoice does not auto-populate the exchange rates yet.
The exchange rate is recorded as the number of base currency units that equal one customer (foreign) currency unit.
Say for example, your base currency is the US dollar (USD), the foreign currency is Euro (EUR) and the exchange rate is 1.28. In Zoho Invoice this is recorded as 1 EUR (one unit of foreign currency) = 1.28 units of USD (your base currency).
Zoho Invoice FAQ