Invite codes and early access
Pine is in early access, and creating an account currently requires an invite code. The signup page asks for the code before you pick your username.
Invite codes are single-use. If yours does not work it has probably been used already; codes are not case-sensitive tricks or rate-limited puzzles, so a rejected code usually just means it was already redeemed.
To request an invite, write to david@pinespace.com.