When creating a merchant billingCurrency and countryCode is defined
countryCode: The country of the merchant. Will be used for invoicing between PSP and MobilePay if billingCurrency is not set.
billingCurrency: If the merchant is invoiced by the PSP in a currency of another country than given in countryCode you can give this invoice currency here. It will 'override' countryCode when we make your invoice.
When initiating a payment currencyCode is defined
currencyCode: This defines the currency of the payment, and will not influence billing.