All Ariana Grande fans who attended the pop star's targeted Manchester Arena gig will be given free passes to Sunday's benefit concert regardless of where they purchased their tickets.
Registration to apply for the free tickets has been extended for those who were at last week's event when suicide bomber Salman Abedi detonated a device, killing 22 people and injuring dozens of others as fans left the venue.
Following the attack, Grande vowed to return to the city and this Sunday will be joined by a host of other music stars including Justin Bieber, Katy Perry, Coldplay, Take That and Miley Cyrus for the One Love Manchester benefit concert at the Old Trafford cricket ground.
Concerns had been raised by those who purchased their initial Grande tickets through third party websites such as Viagogo or Get Me In that they would not receive free passes to the fundraising event.
The initial registration for the free tickets closed at 4pm on Wednesday; however, Ticketmaster said that would now be extended until 2pm on Thursday for "all fans who were at the show, regardless of where they bought their tickets".
In a statement they said: "We understand that there are a number of fans who didn't receive an email this morning with regards to free tickets for One Love Manchester.
"We worked through the night and verified thousands of original bookings although there were some we could not verify.
"To help us verify that fans were at the show, they must register on this link https://manchester_benefit.ontouraccess.com/ and provide their booking reference and information about where they bought their ticket, including the venue box office, or primary and secondary ticketing websites.
"We would like to reassure any fans that were at the show that they will receive a free ticket for One Love Manchester, provided we can verify their initial booking."
On Thursday morning, general sale tickets for the all-star benefit concert sold out in less than 20 minutes. Ticketmaster's website struggled under the weight of massive demand, with 140,000 fans attempting to snap up the £40 tickets online, and many shared screengrabs of the site crashing on Twitter.
Others were pleased to get the opportunity to remember those who died or were injured in the attack, with Joel Hernon celebrating buying tickets by saying he felt "so honoured to have the opportunity to celebrate Manchester's strength on Sunday".
Another user, Karl, wrote: "Over the moon to be attending One Love Manchester on Sunday and not forgetting that we are supporting those affected."
Ticketmaster said: "With over 450,000 searches on our site for One Love Manchester over the last 24 hours, demand was always going to be extremely high."
They confirmed secondary ticket sites such as Viagogo had agreed not to resell tickets for the benefit concert on their websites.
All net ticket proceeds of the show will go directly to the We Love Manchester Emergency Fund, set up by Manchester City Council in partnership with the British Red Cross to support grieving families and victims of the attack.
Belfast-owned live events company Central Fusion, which will be operating all the bars at the concert, will also be donating its profits to the fund.