Why is Player:IsInGroup returning nil??

So I wanted to make like a Gui that would give stuff if you are in a particular group. Since I am using local Script for Gui's, I decided to use Remote Function to get if a player is in group or not since that feature only works in server script.

The thing is that my conditional statement does not seem to be working. The Remote Function instead of returning true or false, it seems to return nil.

Have I somehow messed up writing the parameter?

-- Server Script
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local RemoteFunctions = ReplicatedStorage:WaitForChild("RemoteFunctions")
local GetPlayerGroupInfo = RemoteFunctions:WaitForChild("GetPlayerGroupInfo")

local function GetPlayerGroupData (player)
    return player:IsInGroup(0000000) -- I just wrote it like that :P
end

GetPlayerGroupInfo.OnServerInvoke = GetPlayerGroupData

-- Client Script
GetPlayerGroupInfo:InvokeServer()
local GetPlayerValue = GetPlayerGroupInfo

if GetPlayerValue == true then
    print("Local Player in Group")
elseif GetPlayerValue == false then 
    print("Local Player not in Group")
else
    print("Not Working")
end

It seems to be printing the else statement; Not Working. What am I doing wrong here????