I understand that in order to create invoices in a currency other than your base currency, that currency must be assigned to a contact and then an invoice created against that contact.

In the web interface, I can see how this is done. However, I do not see how this can be achieved via the API (though I was assured it could be by a customer service rep when first enquiring about the limits of Zoho's API).

Can somebody advise RE assigning a currency to a contact via the API through which they are also created, or on an alternate method?

We transact (invoice and receive payments) in GBP and USD so this is essential for us, and given our volume must be achievable by using the API.