Simone Hallmanns Ev Berer Apple Pay asks for the card verification code on adding a card manually. THIS IS NOT YOUR PIN! You can find the verification code in the bunq app, it is 3 digits long and shows on the lower right on every card in the card overview as well as the card details :)
As someone else already said, if you want to add the card in an iPhone or Apple Watch, just add it right from the bunq app.
Hope this helps ✌️