I was coming back from Mill Hill Broadway to Kentish town and tapped my oyster at the machine (there are no barriers). Turns out the machine never read my oyster, even though I had enough money for the journey. I was checked on the train for a ticket, which showed that I had no entry for the journey and was thus travelling without a ticket.
The officer asked me to pay a partial/full fine by cash or card but I did not have sufficient funds on me. He then took a statement from me about the incident and said I will hear from the company soon.