It’s a trap!
If you can, please just wait for version 6.200. It does things the “right*” way, and uses OAuth.
Google does this because they want you to enable what they falsely call “2-factor authentication”. They’ve been pestering people about sharing their phone number with them for years.
In reality, since the so-called second factor is on the same exact device, it’s not two-factors but twice the same factor, and adds no security whatsoever. It is very good at looking like it does, though.
In reality, the purpose of this is, to link your phone and e-mail address more tightly in their ad profile about you, to know more about you, so they know better how to manipulate you (“advertisement”) to effectively steal more money from you (by making you pick inferior choices to their advantage and buy stuff you didn’t need).
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* Of course, the actual right way, is to run a ~$20 home server with your own e-mail client, or at least rent from a provider where you’re the client, and not the product. Especially since it’s gonna cost you anyway, whether through privacy prostitution or just by paying honest provider.