Can't login due to "This browser or app may not be secure"

I'm using the `GIDSignIn.sharedInstance.signIn` to let my app users login with their google account and it works well for most of the cases.

But recently I got a report from one of the users seeing the "**Couldn't sign you in**" error page when logging in saying "**This browser or app may not be secure. Try using a different browser. If you're already using a supported browser, you can try again to sign in.**".

What is the reason for this error and what can I do to solve it? I'm not in control of the way `GIDSignIn` is displaying in-app Safari instance.