How do I fix Sit : param is not a Humanoid or humanoid is dead?

-- In a server script inside ServerScriptService.

local players = game:GetService("Players") -- Players service
local seat = workspace:WaitForChild("MainSeat") 

players.PlayerAdded:Connect(function(plr)
  local char = plr.Character or plr.CharacterAdded:Wait()
  local hum = char:FindFirstChildOfClass("Humanoid") -- The Humanoid
  
  seat:Sit(hum);
end)

That is the code I used that someone helped me write. it's supposed to make a player sit down when they join but I get this error please help me fix this and anymore errors you can spot thanks :)