Istanbul E-pass is available to use 2 years after purhase. E-pass will be activated with first use. Purchase your E-pass and make your plans, make reservations to reservation required attractions. If your trip date changes, you can cancel your reservations or change the dates. If your trip cancel and you don't think you will be able to visit in 2 years, you can ask to cancel your E-pass and get refund.
To cancel your E-pass; only rule the pass shouldn't be used and if any attraction is reserved should be canceled 24 hours before usage date. After your contact with support team for cancelation, your E-pass will be deactivated and refund procedure will start. It generaly takes 5 to 10 business days to see in account.