Have you tried publishing the game and testing on roblox itself, instead of using roblox studio test function? – It’s a reach but it might be a solution
Also, just make sure to actually load the player:
local player = game.Players.LocalPlayer
local char = player.Character or player.CharacterAdded:Wait()
local hum = char:WaitForChild("Humanoid")
Upon testing, I found that it only works when “Avatar Type” is set to R6 in Game Settings, did you design the animation in r6 and are trying to use it in r15?