Solution 1: Please log in to your Google+ account and confirm possible confirmation-queries.
Solution 2: Make sure that the two-factor authentication is deactivated. If you want to keep it activated for your account, you can create a new account and assign the admin role seperately (see: https://support.google.com/business/answer/4573962?hl=en)
Solution 3: At first, please log in to your Google-Account. Please go to the site: 'unlock captcha (https://accounts.google.com/unlockcaptcha )' Here you will find the security settings page for your Google+ Account. You are now being forwarded to a security query. By confirming the query, your account will be connected to our plugin after you got a note, that your access to Google+ is activated.