However, only one payment method can be set as a default and that one will be used on all newly open reservations, but you are able to change the payment method manually.
How to change the payment method
Go to Work > Reservations and select a reservation. Your payment method is shown under Invoice detail (1.).
To change the payment method click on Payment method select (1.) and select the payment method you wish (2.)
Once the Terms of payment, Banking details and Note reload (1.) press Apply (2.) to save the changes.