Pyttsx3 not saving MP3

Here is my code:

    mp3_path = filedialog.asksaveasfile(filetypes=(("MP3 files", "*.mp3"),
                                                   ("All files", "*.*")))  # User prompt to select a path.

    engine = pyttsx3.init()  # A pyttsx3 object

    engine.setProperty('rate', 100)  # Set speed to speed given in entry

    engine.save_to_file('Hi and welcome to my audiobook.', mp3_path)  # Save mp3 to specified path
    engine.runAndWait()

Now, when I try to save the MP3, it doesn't work and the mp3 is empty. I copied and pasted the doc example but it still doesn't work.

I am using MacOS so installing espeak-ng is not needed too.

I didn't figure out the problem, so I just used gTTS. Overall, gTTS is easier to use, BUT with pyttsx3 allows you to customize speed and other things unlike gTTS. Here is the code I used:

mp3_path = filedialog.asksaveasfilename(filetypes=(("MP3 files", "*.mp3"),
                                               ("All files", "*.*")))  # User prompt to select a path.

# Use gTTS library to manage text to speech conversion
tts = gTTS(text=text, lang='en')  # gTTS Object
tts.save(mp3_path)  # Save gTTS object to specified path

As visible using gTTS cut the code by a lot but I am not defining speed.