Why was I charged with a full price using my NS Flex subscription card?

Hi, I am currently subscribing to NS Flex Dal Voordeel which is supposed to give me 40% on my trips during off-peak hours. However, from my account I noticed that the amount charged to my subscription account here: (Also look at the time, it’s considered off-peak hour:

Was the same as the price I had paid with a debit card, from the same place to the same destination, which did not allow for a discount (I had to pay the full price):

I noticed this happened a few times as well, when I traveled on off-peak hours with my NS card with that subscription, I was not charged with the discounted price. Could anyone enlighten me about this? How does the discounted fare work? Thanks.