Unlike Facebook, Twitter and other networks Google and Pinterest don’t have free built-in APIs to make automated posts. You need to obtain a third party libraries to be able to post to Pinterest and Google+
If you already have API files just upload them to the /inc/apis/ folder.
Google+ and Pinterest API libraries along with SNAP Pro WordPress Plugin of the plugin are currently available for purchase for $49 from here: https://www.nextscripts.com/social-networks-auto-poster-for-wp-multiple-accounts/#getit
No separate installation is required, all necessary API files will be automatically installed with SNAP Pro WordPress Plugin.