The white peaks of Mount Hallasan on Jeju Island has gained notable popularity this winter, promoting hikers to pay extra cash to get access to the snowy landscape.

Dozens of postings seeking to sell, buy or exchange QR tickets to Hallasan National Park have been posted at secondhand online stores. Offered by the national park, tickets are available online for free on a first come first serve basis.

One post uploaded on Joonggonara, the country‘s largest online used goods marketplace, showed a user who tried to buy two tickets for 50,000 won ($42) to visit the mountain on Jan. 20. Two tickets for hiking on Jan. 17 are available for exchange, the user added.

The online reservation site, run by Hallasan National Park Management Office, said visiting the mountain trails will be valid only for those who legitimately obtained a QR code by reserving through the website.

“An entry ban will be imposed for a year if one enters with someone else’s QR code,” read an announcement.

The measure comes as the competition for booking gets fiercer, with the website crashing several times a day due to a high traffic.

The reservation system for visiting Hallasan National Park has been implemented since last year to preserve a sustainable natural ecosystem by accepting a limited number of visitors. The number of visitors per day is limited to 1,000 people on the Seongpanak Trail, and to 500 on the Gwaneumsa Trail.