if somebody have the problem that NPC headshots count as normal Headshot so u need change in the plugin line 451 from
if (info.isHeadshot && configData.ChallengeSettings[Challenges.Headshots].Enabled && !attacker.IsNpc)

to

if (info.isHeadshot && configData.ChallengeSettings[Challenges.Headshots].Enabled && !victim.IsNpc)