This key is part of the triple pack from Green Man Gaming.
https://www.steamgifts.com/discussion/r5cUj/castlevania-triple-pack-for-299-restocked-again
Restricted Region !!! This package can NOT be purchased in specified countries
Bhutan, Brunei Darussalam, Cambodia, China, Hong Kong, Indonesia, Japan, Republic of Korea, Lao People's Democratic Republic, Macau, Malaysia, Maldives, Mongolia, Nepal, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, Vietnam, Myanmar, Timor-Leste
