Once you have purchased a ticket, the purchase will appear in a new page underneath the bookings section (entitled Tickets & Permits) of the dashboard when logged into your JustPark account on a desktop device. This page also contains a link to buy a new ticket. This option only appears in the bookings dropdown once you have made a purchase. Alternatively, just visit this link: www.justpark.com/dashboard/season-tickets/
From here, you can check how many usages you have left as well as download a receipt for your purchase, if required.
Please note that you have 730 days to use up all your usages.