On the Project > Options > Currency > Billing Tab
Please Enable Multi Currency Billing, then select Revenue Transaction Currency and select according to your need.
Invoice By Billing Transaction currency :
When the Invoice by Billing Transaction Currency is enabled for the project, you can generate separate invoices for a project by each billing transaction currency, even
though one or more invoices may be funded by the same agreement. Therefore, expenditures that are billed using markups or burden schedules to derive the bill
amounts are grouped according to their expenditure transaction currencies.
Revenue Transaction Currency options for your project :
Oracle Project Billing selects the Project Functional Currency Only option for revenue transaction currency. This ensures that the Generate Draft Revenue concurrent program generates revenue in project functional currency. To enable the Generate Draft Revenue concurrent program to additionally derive revenue in invoice transaction currency.
Project Functional Currency and Invoice Transaction Currency option :
When you select Project Functional Currency and Invoice Transaction Currency as your revenue transaction currency, the Generate Revenue Accounting Events process calculates Unbilled receivables and Unearned revenue amounts in invoice transaction currency.