New Mollie API

Mollie has released a new API that supports multiple payment methods through 1 interface. See documentation: https://www.mollie.nl/files/documentatie/payments-api.html

They now support ideal, mister cash (Belgium) and credit card. 

I'm working on implementing this but it will be a BC break as the whole api has changed.

How can we do this? Release a new major version?

/ping @adrianmacneil