Muckafutha
Member
I'm not sure how they work in their back end, and that's not my problem to know. However, I have personally tested to see if it will 'credit' a top-up to my card if I don't maintain enough funds in my bank account. Guess what, my Giro farecard don't work. So whether it does a direct debit or not it's not my issue. Your question is whether it's a credit system or not, I'm not sure too, but it is confirmed that if you don't maintain enough funds in your bank account, for sure it will not top up for you.
"Cardholders whose bank or credit/debit card account have insufficient funds or insufficient credit limit to effect a deduction for the Auto top-up will find their cards automatically blocked from further use.
When an Auto top-up enabled card is blocked, all other associated cards linked to the same account can continue to be used while there is remaining value, but cannot be auto top-up until the unpaid top-up is settled." source Transitlink
Maybe there was a card that was already blocked so when your own card needed a top up it didnt work.