To redeem a promo code, be sure to enter it in the “promo code” field when you are searching for tickets and your discount will be automatically applied.
Please ensure to read the restrictions of your promo code before applying- All promo codes are different and they require set parameters to book and or 7 day advanced bookings.
Before clicking on "Search Tickets" , click on "Add a Promo Code" at bottom of the train ticket search.
Then, click "Apply," and search tickets. The ticket results should show a crossed out fare and a new fare next to it. This is how you know the promo code applied, successfully. See the highlighted fare, below.