Found this: github.com/sponsors/twingyeo-kr.

A quick translation says:

Hello, twingyeo.kr is a Mastodon instance operated by Team Onstables Co., Ltd. Currently, in order to create a ‘space where everyone can rest comfortably’, our instance is covering all operating costs with the income from the software development sector of Team Unstablers Co., Ltd., the main operator, without any means of generating profits such as advertising.

Maybe the instance is down that’s why it’s unreachable.