So BTS and its peers have been forced to sneak in via the internet. One important entry point has been Coca-Cola FM, the soda giant’s online radio platform, which is largely unknown to American audiences but popular in Chile, with an estimated daily listenership of 40,000. Every Friday, the network runs a K-pop program hosted by a Chilean D.J., Rodrigo Gallina. Social media has played a tremendous role, too: BTS has more than five million Twitter followers, and to date BTS has spent 22 weeks at No. 1 on Billboard’s Social 50 chart, which ranks the global online activity of artists’ social-media fan pages and weekly song plays. A dedicated BTS Chile Twitter account, run by three fans, regularly posts Spanish translations of news articles about the band and of the band’s own posts on social media. Some Chilean fans tune in directly to Korea’s popular V app, where artists hold live-streaming broadcasts that fans anywhere in the world can join and ask questions (BTS’s channel has more than 4.7 million followers).

The band’s online popularity had become so entrenched in Chile that tour promoters didn’t even bother with a traditional media push. Fans waited outside the arena box office to purchase tickets, which ranged from $38 to $212, for up to a week in advance. All 12,500 tickets for what was supposed to be just one show sold out in a record-breaking two hours. “The speed of those sales made us immediately begin preparations for a second show,” says Gonzalo Garcia, the C.E.O. and founder of NoiX Productions, which focuses strictly on bringing Asian artists to Chile and other Latin American countries. Eventually, NoiX ran eight days of print ads in the daily newspaper La Tercera, but simply as a thank-you to fans who had bought tickets.

The Backstreet Boys, One Direction and the Jonas Brothers have all played in Chile, but Korean boy bands are a recent phenomenon, having begun to visit the country only since 2012. Before its performances last month, BTS did play a show in Chile on its last tour in August 2015, but promoters booked only about half of the Movistar Arena. In the months since, though, the group’s popularity has skyrocketed in the K-pop world — the “Wings” album was South Korea’s best-selling album of 2016 — with fans worldwide seeming to connect with the band’s increasingly polished sound and relatable-yet-hopeful messages. “We talk about our own turmoil and mental breakdowns as honestly as possible in the music and [how] it grows with us as we get older,” the band member Rap Monster says. “We believe Chilean fans tend to connect to those values, maybe a little deeper than fans in other countries,” he added.

The band’s delighted handlers struggle to find adequate metrics to capture the extent of BTS mania in Chile. There is money, of course; Garcia says ticket sales from this year’s two-day concert series “exceeded the $2 million mark,” and this figure doesn’t even include revenue from the enormous amount of BTS merchandise (like a $45 glowing light stick or a hand-held fan with the members’ faces printed on it for $9) sold at the arena. For BTS’s South Korean record label, Big Hit Entertainment, the most remarkable measure is online engagement, which it seems to monitor very closely. “We crosschecked with social-media-channel statistics to confirm the level of loyalty and fan base in the country,” says Yandi Park, a concert business manager for Big Hit. “We did expect to have good ticket sales because the promoters were also confident ... but did not anticipate the sellout in minutes.” Then there are the organic expressions of fan fervor: In parks and public sites throughout Chile, thousands of fans have begun to gather frequently to learn K-pop dances together.