A waiting list could help fill released places, while an authorised transfer process could let a ticket holder pass admission to someone else under the organiser's rules. These are related workflows, but neither should leave two valid copies of one ticket.
Offers from a waiting list need a time limit and a clear acceptance step. A transfer may require approval, a name change or payment through the platform. Once completed, the original admission code should be invalidated or otherwise handled consistently by the entry system.
Define the rules before building the screens. Test an expired offer, a cancelled transfer and a ticket already scanned at the venue. Keep a history for support staff so they can identify the current holder and explain what happened without relying on forwarded emails.
Related reading: Events Business Software Solutions.