I've tried both with my card and with PayPal.
The PayPal transaction looks like any normal transaction -- goes to the paypal page, asks me to login and select which payment method I want to do, then says "redirecting to the merchant" (or something).
Then it goes back to the "select a payment method" screen on Mollie. My card doesn't get charged and nothing shows up on my PayPal account.
I also tried paying by card, but it gives an error "the card you have used is incompatible with this payment method".
My card and PayPal account are both definitely fine and I've been able to buy other things through PayPal successfully today.
I'm in Australia, I tried paying both with PayPal converting to AUD and with PayPal not converting the currency.