Originally Posted by ffgap

I used a prepaid contactless card via Google Pay on TfL. Accidentally, I made another purchase on that card (which was supposed to go to another card on G Pay) which brought my balance virtually to zero. Before I noticed, TfL tried to debit the card and the payment was declined...

What is the consequence? Of course, after noticing, I loaded some cash on the card. But I am wondering if I am liable for a penalty fare?