I tried to buy my STEP ticket, but it says my code has already been used
If you selected tickets on the event page and clicked Order Now then closed the page, hit back in your browser or had a failed purchase attempt, you'll see the message 'Promotion code has already been used'. Quicket has marked your code or ticket link as invalid for 15 minutes to ensure that the code cannot be used again while you are going through the checkout process.
As long as the order was not completed or successful, your code will become valid again 15 minutes after you clicked Order Now. Please be patient and wait 15 minutes; you will be able to use your ticket link or code again after that time.