At this link, fill in name and email and click 'Doorgaan'
https://payments.wikimedia.org/index.php?title=Special:AdyenGateway&appeal=JimmyQuote&ffname=adyen&payment_method=rtbt&payment_submethod=rtbt_ideal&recurring=&uselang=nl&language=nl¤cy=EUR&amount=1.5&country=NL
Then on the iDEAL page click 'terug' at the bottom of the page. The resulting error message (on paymentswiki) is in English when it should be in Dutch.