Gmail, like all other email service providers is strongly committed to protecting its users from suspicious activities because of password theft. Google alerts you when your Gmail credentials have been used by an unknown application. So when you try to connect your Gmail account with Freshsales, you receive an email from Google with the subject Sign-in attempt prevented.
All you’ve got to do is grant Freshsales access to your Gmail account by either turning on access for less secure apps or by generating an app password.
This email reaches you soon after you attempt to sign into Gmail from Freshsales. If you've got more than one email from Google with the same subject (Sign-in attempt prevented), the latest email should be the one about Freshsales.
Learn more from this article.