"Ik heb geen contant geld, maar wel een pinpas."
Translation:I have no cash, but I do have a debit card.
I'm not native, but I think it's an affirmative to counter "geen". The way I think about it is : I have no cash, but "yes" a debit card. I think in Dutch you've already said I so there's no need to use it again, but you need some word to note that you DO have a debit card even though you don't have cash and that's where "wel" comes in.