"Please do not attempt to sell #OneLoveManchester tickets on our site".
The listing was taken down shortly after being seen by the Press Association. But, as one person pointed out on Twitter, the tickets are popping up on resale websites for a lot more than that.
Ticketmaster said tickets to the event sold out within 20 minutes.
Some tickets were held aside for those who had attended the May 22 Grande concert, at which 22 were killed and scores wounded.
Some tickets for the benefit concert have appeared on eBay - but the company has told the BBC it is attempting to remove listings as soon as they appear.
All proceeds will benefit the We Love Manchester Emergency Fund, which was founded by the Manchester City Council, in conjunction with the British Red Cross, to aid victims of the attack and their families.
"We also aren't allowing the sale of any item which profits in any way from the tragedy in Manchester".
Tickets were offered at no charge to people who had been at the show that night, with the rest going on sale to the general public at £40 a piece.
Beyond the venue, the event will be live broadcast on BBC Television, BBC Radio, and Capitol Radio Networks.