The card costs £30 each year, with many users saving the cost of the card within just one or two journeys.
If you're one of the lucky ones to get one of the first 10,000 cards you need to be armed with some information to process your application.
The 26-30 Railcard won't apply to season tickets, Eurostar, and most London Underground and Docklands Light Railway tickets - unless using Oyster pay-as-you-go.
The new railcard went on sale on Tuesday, 13th March, and if you only turn 31 on Wednesday, 14th March, you are still eligible to buy the new railcard. "Please bear with us, we've got the whole team working on it and hope we can have it back up shortly", said a spokesperson for railcard.co.uk.
Hours after the tickets were released, the National Railcards Twitter account issued an update, reassuring users that the railcards had not yet sold out.
Tom Drury, from London, wrote: 'The launch of the new railcard is a shambles'.
A pilot programme has been running in the Greater Anglia area since December 2017, also involving 10,000 railcards.
Harriot Bishop wrote on Twitter: "Trying to get a 26-30 Railcard is about as painful as trying to get tickets for Take That's Progress tour in 2010 (and this is the least millennial reference you'll see on the subject today)".
The trial of the 26-30 railcard is part of the rail industry's long-term plan to change, improve and boost communities by enabling more people to travel by train.
This new card costs £30 per year and will only be available digitally, meant to be used on smartphones.
Between 04:30 and 10:00 Monday to Friday, a £12 minimum fare will apply.
"Research being gathered as part of the 26-30 Railcard trial expansion is being used to inform discussions with the government about a national roll out".
The scheme is now being trialledto assess the impact on revenue and passenger numbers, meaning only 10,000 are now available.
The millennial railcard announced in Philip Hammond's last Autumn Budget largely grants those aged 26-30 the same privileges as holders of the 16-25 railcard; that is, a third off all travel.
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.