Can't pass objects from client-server?

Hello there,

I am working on my game right now, and just started working on the engine this week. I have a function that creates an object on the server, and then returns that object. It seems to work fine when I am returning the object from the server to the client, however, the part does not get returned when the situation is flipped around. I tried to return a part made on the client, but it wouldn't return the object and just kept returning nil.

So I am wondering if this is because of a roblox issue and I need to find an alternative to accomplish this task, or is it just something wrong with my code. I will post the code below so you can analyze exactly what I mean.

-- Server - Client Function --
local rs = game:GetService("ReplicatedStorage")
local folder = rs:WaitForChild("Instance Work")
local instance_func = folder:WaitForChild("Instance")

------------------------------------------------------	
	-- Creates a part on the server --

local function instance(plr, obj, props)
	local object = Instance.new(obj)
	
	for prop, value in next, props do
		if prop == 'Parent' then
			value = return_obj_from_string(value)
		end
		
		object[prop] = value
	end
	
	if object then return object end
end

instance_func.OnServerInvoke = instance

	-- Creates a part on the server --
------------------------------------------------------

####The above will create an object on the server and then successfully return that object to the client.

-- Client - Server Function --
local rs = game:GetService("ReplicatedStorage")
local folder = rs:WaitForChild("Instance Work")
local instance_func = folder:WaitForChild("Instance")
------------------------------------------------------	
	-- Creates a part on the client --

local function instance(obj, props)
	local object = Instance.new(obj)
	
	for prop, value in next, props do
		if prop == 'Parent' then
			value = return_obj_from_string(value)
		end
		
		object[prop] = value
	end
	
	if object then return object end
end

instance_func.OnClientInvoke = instance

	-- Creates a part on the client --
------------------------------------------------------

####The above creates an object on the client, however, it fails to return the object to the server.

####The code below is how I made the call to the client from the server and how it failed to return the part.

-- Script inside Click Detector, which is inside a part and meant to activate the client function upon clicking the part --
local detector = script.Parent;
local rs = game:GetService("ReplicatedStorage");
local instance_folder = rs:WaitForChild("Instance Work")
local instance = instance_folder:WaitForChild("Instance")

detector.MouseClick:Connect(function(plr)
	local char = plr.Character or plr.CharacterAdded:Wait();
	local root = char:WaitForChild("HumanoidRootPart");
	local props = {
		['BrickColor'] = BrickColor:random();
		['Transparency'] = math.random();
		['Anchored'] = true;
		['CanCollide'] = false;
		['Material'] = Enum.Material.Neon;
		['CFrame'] = root.CFrame;
		['Parent'] = workspace;
		['Name'] = 'Innovation';
	}
	print("It is:", instance:InvokeClient(plr, 'Part', props)) -- Prints "It is: nil"
end)

##Thank you for any help and hope you have a nice day/night.

Best regards,

IdealistDeveloper