On the first day I landed at Busan Airport, I couldn't use the esim, so I went to the SK staff at the counter. The staff took about 20 minutes to help me, so I was able to use it. The internet was fast and didn't lag. It was okay, worth the price.
Traveloka Sdn Bhd (Registration No. 201501003122), Level 14 Tower 2, Menara Kembar Bank Rakyat, 33 Jalan Rakyat Brickfields, 50470 Kuala Lumpur, Malaysia