There is a note in google identity platform document:
https://developers.google.com/identity/protocols/oauth2/openid-connect
Note: If you want to provide a "Sign-in with Google" button for your website or app, we recommend using Google Sign-In, our sign-in client library that is built on the OpenID Connect protocol and provides OpenID Connect formatted ID Tokens.
As I understand, google using OpenID Connect for sign-in library, which means the pricing tier for this is tier 2 according to this page:
https://cloud.google.com/identity-platform/pricing
and I will have to pay if there are more than 50 people sign in to my site each month, Please help me to confirm if this is correct.