Why is error given when trying to add to kills leaderstat?

I am making a gun that adds to your kills leaderstats when you get a kill but it gives me an error when i try to change the leaderstat and I do not know how to give a number to the kills leaderstats once the target is at 0 health

local deagle = script.Parent

deagle.Shoot.OnServerEvent:Connect(function(player,mousePos)
    local raycastParams = RaycastParams.new()
    raycastParams.FilterDescendantsInstances = {player.Character}
    raycastParams.FilterType = Enum.RaycastFilterType.Blacklist


    local raycastResult = workspace:Raycast(deagle.Handle.Position,(mousePos - deagle.Handle.Position)*2147000,raycastParams)

    deagle.Handle.GunShot:Play()
    if raycastResult then
        local hitPart = raycastResult.Instance
        local model = hitPart:FindFirstAncestorOfClass("Model")

        if model then
            if model:FindFirstChild("Humanoid") then
                model.Humanoid.Health -= 36
                if model.Humanoid.Health == 0 then
                    player.leaderstats.Kills = player.leaderstats.Kills + 1
                end 
            end
        end
    end
end)