Your problem is you put None in your variable enter_mess_here here:
enter_mess_here = tk.Entry(root).pack() #getting error here
and in your function when you want to get the value it's not getting value from Entry it's getting from Nothing. So it raises an error.
First assign your Entry to a variable then use pack, so this will work:
enter_mess_here = tk.Entry(root)
enter_mess_here.pack()
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