Field help (CURSIH) 

The currency proposed is the one associated with the bill-to customer in the customer record if the invoice is direct, or the one linked with the original document. It is modifiable during copying or during creation. The modification of the currency then leads to the display of a message proposing the recalculation of prices and discounts based on the price lists. It the price lists are not to be applied, the prices and discounts will simply be converted into the new currency at the invoice exchange rate. This information can no longer be accessed once a line is entered in the invoice.

From this field, it is possible to directly enter a currency code whose existence is controlled in the currency table or to use the contextual button to: