When creating a customer invoice, how to set payment method / custom fields ?

Is there a way to set payment method (transfer, credit card,...) when creating invoice from API ?

As it is possible with the gui editor, It would be greatly appreciated to have a way.
And if not possible yet, any possibility to give custom fields previously created in Invoice templates. ?
For ex; get the invoice template with custom fields ids. Then create the invoice request giving the invoice template id and the field ids => data.

Thanks in advance for your reply