What do Koreans use instead of Paypal?

Excuse me, I'm curious about a matter related to finance in Korea. I know Paypal is a widely used online payment system in many countries, but I'm not sure about its popularity in Korea. So, my question is, what do Koreans primarily use as an alternative to Paypal for online transactions or making payments? I'm interested in understanding the preferred payment methods in this region and how they differ from other parts of the world.