How to Buy a Friend (Korean: 계약우정) is a 2020 South Korean television series starring Lee Shin-young, Shin Seung-ho, Kim So-hye, Oh Hee-joon, Min Do-hee, and Cho Yi-hyun. Based on the Daum webtoon Friendship Contract by Laad Kwon, it aired on KBS2 from April 6 to 14, 2020.

Kim So-hye, known mononymously as Sohye, is a South Korean actress and singer under S&P Entertainment. She is a former member of the girl group I.O.I, finishing fifth on Mnet's survival show Produce 101. She is best known on her acting roles in Poetry Story (2017), Kang Deok-soon's Love History (2017), Best Chicken (2019) and My Lovely Boxer (2023).