You could look on platforms like MangaFox or MangaHere. Sometimes, these sites have 'What's Wrong with Secretary Kim' manga. Just be cautious of pop-up ads and ensure your device has good security software.
I'm not sure about specific places for free reading. Usually, authorized platforms require a subscription or purchase. But sometimes, there could be limited-time promotions or free chapters on official sites.
Maybe the plot development is a bit confusing or the character designs don't appeal to everyone. It could also be that the story pace is off for some readers.
Perhaps there are issues with the consistency of the world-building or the way the relationships between characters are portrayed. Also, the level of drama or comedy might not hit the right mark for some.
Could be various things. Maybe the storylines are too predictable, or the romance aspect isn't developed well enough. Different people might have different complaints about it.