attempt to perform arithmetic (sub) on nil and Vector3? On FireClient

So I was just passing my mouse position and my shoopart onto my clientside bullet, but this error keeps on repeating and I dont know why. Can anyone please help me with this?

Server:

bullet.OnServerEvent:Connect(function(player, mospos, startbul)-- the mouse position and shootpart or start of bullet
    local origin = startbul.Position
    local direction = ( mospos -origin).Unit
    local params = RaycastParams.new()
    params.FilterDescendantsInstances = {script.Parent, script.Parent.Parent}
    params.FilterType = Enum.RaycastFilterType.Blacklist
    params.IgnoreWater = true

    local result = workspace:Raycast(origin, direction*200, params)
    if result then
        local hum = result.Instance.Parent:FindFirstChild("Humanoid")
        if hum then
            hum:TakeDamage(30)
        end
    end



    for i,v in pairs(game:GetService("Players"):GetPlayers()) do
            bullet:FireClient(v, mospos, startbul)
        end

end)

Client:

bullets.OnClientEvent:Connect(function(Players, mousepos, startofbullet)
    local bullet_clone = clientbullet:Clone()
    local params = RaycastParams.new()
    params.FilterDescendantsInstances = {script.Parent.Parent,game.Workspace:WaitForChild("laserbulletsfolder")}
    params.FilterType = Enum.RaycastFilterType.Blacklist
    laser.lasersound:Play()
    local origin = startofbullet
    local direction = (mousepos - origin).Unit -- the error shows here 
    local result = workspace:Raycast(origin, direction*200, params)
    if result then
        print("Client Side: ", result.Instance)
    end
    local intersection = result and result.Position or origin + direction*200
    local distance = (origin - intersection).Magnitude

    bullet_clone.Size = Vector3.new(0.1, 0.1, distance)
    bullet_clone.CFrame = CFrame.new(origin, intersection)*CFrame.new(0, 0, -distance/2)
    bullet_clone.Parent = game.Workspace:WaitForChild("laserbulletsfolder") or Instance.new("Folder", game.Workspace)
    game.Debris:AddItem(bullet_clone, 0.07)

end)

ERROR:

Players.Character.Backpack.laser.clientside:22: attempt to perform arithmetic (sub) on nil and Vector3  -  Client - clientside:22
  08:50:23.279  Stack Begin  -  Studio
  08:50:23.279  Script 'Players.Character.Backpack.laser.clientside', Line 22  -  Studio - clientside:22
  08:50:23.279  Stack End  -  Studio