Network Ownership API cannot be called on Anchored parts or parts welded to Anchored parts.

What the message means

ServerScriptService.CarSpawner:14: Network Ownership API cannot be called on Anchored parts or parts welded to Anchored parts.

Other forms of the same message:

• Network Ownership API can only be called from the Server.
• Can only call Network Ownership API on a part that is descendent of Workspace

Network ownership decides which computer simulates a part's physics: the server, or one player's client. Roblox applies it to a whole assembly, the group of parts held together by welds and other rigid joints. If any part of that assembly is anchored, nothing in it moves, the server owns all of it, and the ownership calls refuse to change that.

Two related messages come from the same API. Network Ownership API can only be called from the Server. means a LocalScript called it. Can only call Network Ownership API on a part that is descendent of Workspace means the part is not in the Workspace yet, for example a clone you have not parented.

Causes and fixes

Two things cause this error in practice. Each one below has the smallest code that triggers it, then the fix.

• The part is still anchored when the owner is set
• The part is welded to something anchored

The part is still anchored when the owner is set

Templates in ServerStorage are often anchored so they do not fall when you place them. A spawner that clones the model and sets the owner straight away hits the anchored parts.

local ServerStorage = game:GetService("ServerStorage")
local Players = game:GetService("Players")

local template = ServerStorage:WaitForChild("Car") :: Model

local function spawnCar(player: Player)
	local car = template:Clone()
	car.Parent = workspace
	local seat = car:FindFirstChildWhichIsA("VehicleSeat", true)
	if seat then
		-- the template is anchored: Network Ownership API cannot be called on Anchored parts...
		seat:SetNetworkOwner(player)
	end
end

Players.PlayerAdded:Connect(spawnCar)

Unanchor every part of the model after you place it, then check CanSetNetworkOwnership and set the owner.

local ServerStorage = game:GetService("ServerStorage")
local Players = game:GetService("Players")

local template = ServerStorage:WaitForChild("Car") :: Model

local function spawnCar(player: Player)
	local car = template:Clone()
	car.Parent = workspace
	for _, part in car:GetDescendants() do
		if part:IsA("BasePart") then
			part.Anchored = false
		end
	end
	local seat = car:FindFirstChildWhichIsA("VehicleSeat", true)
	if seat then
		local ok, reason = seat:CanSetNetworkOwnership()
		if ok then
			seat:SetNetworkOwner(player)
		else
			warn("[CarSpawner] cannot set owner:", reason)
		end
	end
end

Players.PlayerAdded:Connect(spawnCar)

The part is welded to something anchored

The part itself is unanchored, but a WeldConstraint, Weld or Motor6D joins it to an anchored part: the map, a building, or one anchored decoration inside the same model. That makes it part of an anchored assembly.

local Players = game:GetService("Players")

local crate = workspace:WaitForChild("Crate") :: BasePart
-- the crate is welded to the anchored dock it sits on
local weld = Instance.new("WeldConstraint")
weld.Part0 = crate
weld.Part1 = workspace:WaitForChild("Dock") :: BasePart
weld.Parent = crate

Players.PlayerAdded:Connect(function(player)
	-- Network Ownership API cannot be called on ... parts welded to Anchored parts.
	crate:SetNetworkOwner(player)
end)

Remove or disable the weld to the anchored part before you hand the part to a player. To find hidden joints, loop over part:GetJoints() in a script and print what each one connects.

local Players = game:GetService("Players")

local crate = workspace:WaitForChild("Crate") :: BasePart

local function freeFromAnchored(part: BasePart)
	for _, joint in part:GetJoints() do
		if joint:IsA("WeldConstraint") then
			local other = if joint.Part0 == part then joint.Part1 else joint.Part0
			if other and other.Anchored then
				joint.Enabled = false
			end
		end
	end
end

Players.PlayerAdded:Connect(function(player: Player)
	freeFromAnchored(crate)
	if crate:CanSetNetworkOwnership() then
		crate:SetNetworkOwner(player)
	end
end)

This example only handles WeldConstraint. Classic Weld and Motor6D joints use Part0 and Part1 too; check those the same way if your model uses them.

How to find the line that causes it

1. Open Output (Window menu, or the Script tab), clear it with Ctrl+K (⌘K on Mac), and press Play.
2. Find the first red line. It starts with the script's place in the Explorer and the line number, such as ServerScriptService.Shop:12:.
3. Click the red line. Studio opens that script with the cursor on the failing line.
4. Read the lines between Stack Begin and Stack End under it: they list the calls that led there, newest first, so you can see which function called the broken one.
5. Still not sure which value is wrong? Add print(typeof(x), x) just above the line, or set a breakpoint on it and read the values in the Watch window.

Questions

Sources and further reading

• Roblox Creator Docs: network ownership. the server always owns anchored parts; ownership applies per assembly
• Roblox Creator Docs: BasePart:CanSetNetworkOwnership
• Roblox Creator Docs: assemblies

How the code was checked: every block marked Fixed passes Luau's strict type checker against Roblox's API definitions (luau-lsp, 4 November 2026), and every block marked Breaks compiles and fails only when it runs. The message wording, and the two related messages, were checked against the message strings in Roblox Studio itself (macOS build installed on 24 October 2026) on 4 November 2026. The ownership rules are from the network ownership page in the Roblox creator docs. A type check catches misspelt APIs and wrong types, not game logic, so playtest in Studio before you publish.