Try another gate reader, there might be a problem with that specific one.
Check that the ticket on your Key hasn't expired, or is valid for the route you're trying to take (such as valid for use on High Speed services or not), as the Key won't work at stations the ticket isn't valid at. You can check your ticket by using the Southeastern app. Go to ‘My Tickets’, choose the ‘Key tickets’ tab, select ‘View card contents’ and hold your Key to the back of your phone. Alternatively, you can hold your Key on the yellow reader of a ticket machine at the station to view it’s contents, or see a member of staff.
If you're still having issues using your Key on at a specific set of gates, please make sure to note the time, location and what the error message/code on the gateline screen says. When you
contact Customer Services, please let them know the code as it may help speed up the resolution for you.
If your Key hasn’t worked at any station for sometime, there is a possibility there may be a problem with the card itself. Whilst Keys are much more durable and reliable than the orange paper tickets, unfortunately they do fail from time to time. You can simply request a new Key from your Southeastern account under "The Key Replacement". You will need to buy alternative tickets while your Key is replaced (may take up to 5 days in the post), but they can refunded if they cover the same validity as your smart ticket.