Demand for the new millennial railcard has crashed the website on the first day of nationwide sales.
The one-year railcard for 26 to 30-year-olds will cost £30 and offer a third off most fares in England, Wales and Scotland.
It first went on sale nationwide at about 07:30 GMT but "exceptional demand" caused the website to fail.
Delays of up to two hours have persisted into the afternoon with some still struggling to get online access.
Only 10,000 railcards are being released during the trial.
"This morning, when the 26-30 railcard trial began, the National Railcard website was receiving 12 times the normal number of visitors. We were prepared for demand to be similar to that of previous trial launches," said a spokeswoman for the Rail Delivery Group, which represents the train companies and Network Rail.
"Due to the unprecedented demand we have been working with our suppliers throughout the morning to further increase the capacity on the website to create a better experience for our customers. We recommend that customers continue trying the National Railcard website, and keep an eye on @_Railcards Twitter and Facebook pages for updates."
The group had earlier apologised for the problems.
Some passengers have been expressing their irritation at the problems.
The limited number of cards - enough for one in 500 of the eligible population - went on sale on Tuesday following a trial across the Greater Anglia network when another 10,000 railcards were sold.
Applications can only be made on the 26-30 railcard website, and holders need to download an app before they can use the card. However, the site states that the service is unavailable when visitors press the "buy" button.
One of those struggling to buy a card is Helen Coffey, deputy head of travel at The Independent. It is her 31st birthday on Wednesday, so this is the last day that she would be eligible to buy the card.
"It is today or it is never," she told BBC Radio 5 Live.
"I don't know if it was the hype that made me want to get one, but I have this one shot, and it seems impossible.
"They were a bit naive to think it would not be flying off the shelves."
David Sidebottom, passenger director at watchdog Transport Focus, said: "The nationwide trial of the 26-30 railcard should be welcome news for passengers facing stagnant or falling incomes but they will be extremely disappointed that they are unable to access the website."
The card does not cover all travel. The discount for some during the morning commute is limited as a minimum fare of £12 applies to all journeys made before 10am, Monday to Friday.
The Rail Delivery Group said discounts were not given on season tickets, but a weekly or monthly season ticket could still be the cheapest option for those in this age bracket who commuted frequently by train.
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