I am experiencing the same issue as everyone else. Initially, the game successfully accepted the key input. However, upon subsequent game launches, it prompted me to enter the key again, followed by the message indicating that the key had already been used.
Viewing post in Boys in the Dark - Bug Fixes & Technical Update comments
Thank you for the detailed report, Atomic. Please make sure you didnt download a cached old version. I've posted a new devlog about this issue <3
https://goldenunicorn.itch.io/boys-in-the-dark/devlog/1517358/new-download-link-...