There are scenes in this drama where Actor Ahn Hyo Seop speaks perfect English that's because he is actually Canadian! His family moved to Toronto, Canada when he was younger. He went by his English name Paul Ahn when he was still residing and studying in Canada. When he was 17, he moved back to South Korea to pursue a career in the entertainment industry.
Based on web novel "Sanae Matsun" by Hae Hwa (published from August 3, 2017 to November 21, 2018 via KakaoPage).
English translations of the webtoon can be read on tapas App under "A Business Proposal." It's an ongoing series.
The cover art for the manhwa can be seen in the bus stop shelter in the first episode.
In two weeks, Kim Sejeong lost 11 pounds to improve her health and gearing up for this drama "A Business Proposal" by going on a diet.