Unlike Facebook, Twitter and most other networks, Google+, Instagram, Reddit, Flipboard and Pinterest don’t have free built-in APIs to make automated posts. You need to obtain third party API libraries to be able to post to Pinterest, Reddit, Flipboard and Google+
Also Blogger and LinkedIn APIs with expanded functionality are available.
All those API libraries along with SNAP Pro WordPress Plugin of the plugin are currently available for purchase for $49 from here: http://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.
PS: If you already have API files that you got from some other source just upload them to the /inc/apis/ folder.