Straight from the official website:
Due to technical issues with the Athenon Arena, it has been decided by the promoters, with the agreement of the artist, to combine the Athinon Arena concerts and move to a larger venue – the Faliro TaeKwonDo Olympic Arena. All tickets for the former 16th and 17th September concerts at Athinon Arena are valid for the concert at the TaeKwonDo Arena. Ticketholders of the former 16th September show who are unable to attend the concert on the 17th can return their tickets for a full refund at the selling-point they purchased them from up till Wednesday 15th of September.
Due to the bigger venue, additional tickets are now on sale at the ticket-selling points.
For more info please check: www.detoxevents.gr