Events often use ticket phases (early bird, regular, late bird etc.). If tickets from a particular phase are sold out, you can no longer buy tickets at a reduced price.
If all tickets are sold out on the official ticketshop of the event, we as ticket partner cannot offer any more tickets. It is also not possible to get on a reserve list in case tickets are cancelled. We recommend keeping an eye on the event's socials/website for any additional sales.
