Viki has not recruited for a channel manager on Moon Lovers – This leads me to suspect that viki has gotten a license only for the presubbed English, Spanish, and French. There is no menu item “Subtitle Team” on the channel page.
The channel has been listed on the project finder for subtitles in Korean for months.
The project finder at viki seems to list everything at vik as available for subbing in some language, even channels no longer available to the channel manager for the channel.