And this is why Cortis's incessant calls to for people to put their phones down have rubbed some the wrong way - in a fan culture that's obsessed with capturing every moment. After the first day of their concert, disgruntled comments emerged online among fans.

"I spent over one million won ($700; £520) attending both days," Park says, referring to the sum of not just concert tickets but also additional expenses like transport and accommodation.

"I think a lot of fans spent similar amounts of money, so constantly hearing them asking us to put our phones down made some fans even more frustrated."

These murmurs appear to have reached Cortis, who fans say dialled down their message on the second day of the concert.

"On the first day, the message felt more like, 'Let's put our phones down and have fun together.' On the second day, it changed slightly to, 'We understand why you want to film, so let's just make sure we enjoy ourselves together,'" Kim recalls.

"They said filming was okay, but they wanted us to enjoy the concert together, and that 'Put Your Phone Down' was more of a mindset."

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