Dennis Nowhere. The online card is not meant for physical payments including Apple Pay, but for online payments only. What’s in the name. ;) That card doesn’t have a PIN set. You have to get a physical MasterCard if you want one with a pincode.
Whilst the online card will function fine in Apple Pay, if any terminal asks for the PIN of the card: you’re out of luck. :P
You could try it with pin 0000, but I bet the chances of that working are very slim.