Hi,
In Belgium, cards do not have a CVV(CVC) number. We are advised to use 000 or 999 for that.
It would smoothen the flow if you did not ask for those numbers if the person signing up has a Belgium phone number or something similar.
A Belgian could still have a non-Belgian card.
Only thing I could imagine is they hide that field once the card in question is identified as Belgian. I wonder though if that could not lead to false positives or negatives.