Mimi?

Where is the NPC Mimi for the 7th Day Market?
I got the quest but it ends due to an 'unknown error'.

Or is she only available on Sundays?

in nlc, if you are moving left towards the market guy, youll see 2 npcs in the mini map, but when you get closer one disappears, the that disappears is Mimi, so it may only show up on sundays.

Ohh she's in NLC?
I've thought she was in Henesys. Lol.

And now once it just hit Saturday, I was able to complete the quest.

she is in henesys too
just look in town for her on any sunday

The NPC's appear and disappear depending on what day it is. She replaces the seller on Sundays to let you into the Market.