HTML PHP google single sign on signout will throw “Cannot read property 'getAuthInstance' of undefined”

Question

I have created google single sign on by following steps mentioned in https://developers.google.com/identity/sign-in/web/sign-in

The sign in works like a charm but when

Answer 1

Check: https://developers.google.com/identity/sign-in/web/reference#gapiauth2getauthinstance

and in particular this part:

gapi.auth2.getAuthInstance()

Returns the GoogleAuth object. You must initialize the GoogleAuth object with gapi.auth2.init() before calling this method.

For me, the problem is that I didn't call gapi.auth2.init() first