Trying to concat GetDescendants of workspace doesn't work

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1 
game.Players.PlayerAdded:Connect(function(add)
    local Tabla = workspace:GetDescendants()
    print(table.concat(Tabla," ",1,#Tabla))

end)

I want to make this script print all of the thing in the workspace. The error is

Workspace.Script:3: invalid value (userdata) at index 1 in table for 'concat'
3

Yes, I know but why doesn’t my script work?