The railcards are available for those aged 26-30, and they give a third off rail travel in the UK.
The cards could be applied for from today but as there are only 10,000 now available, they are being issued on a first-come, first-serve basis, the Rail Delivery Group (RDG) said. "Sort out your website to make it fair!" wrote Emily Thomas, from London.
Thousands of frustrated young adults spent hours trying to get their hands on the new 26-30 railcard, dubbed the millennial railcard, when it launched on Tuesday.
Tom Drury, from London, wrote: "The launch of the new railcard is a shambles".
It must be bought online and downloaded onto a smartphone.
Many felt a cap on the amount of railcards available was thoroughly unfairWhile others were left raging at the amount of time it took to actually get oneSome smug travellers actually did manage to get a card despite lengthy waitBut it didn't seem to have the intended impact on millennials' opinion on politics...
There was previously no nationwide railcard available for people travelling alone between the ages of 26 and 59 unless they were disabled or in the armed forces. "This is due to the exceptionally high volume of traffic on the 26-30 Railcard website". We'll keep you posted here as soon as we resolve the issues. "Please bear with us, we've got the whole team working on it and hope we can have it back up shortly".
Research being gathered as part of the 26-30 railcard trial is being used to inform discussions with the government about a national roll out, and to develop new products that make leisure travel easier and better value for customers.
A spokesperson for the RDG, which represents train operators and Network Rail, said: "We're sorry to those who have been unable to buy a trial 26-30 Railcard this morning".