There was free API for autoposting to groups until Facebook disabled it couple weeks ago. They no longer allow that.
After that, we made our own API for Facebook that could autopost to groups. Our Premium API it’s not free.
“SNAP Pro WordPress plugin” and “NextScripts Premium API” are two completely different products. You can buy and use them together or separately.
“SNAP Pro WordPress plugin” is one time purchase for a lifetime license. You can add multiple accounts for each network and enjoy advanced plugin features for as long as you like. All future updates are included.
“NextScripts Premium API” is a yearly subscription service. It adds an ability to auto-post to networks without native built-in API. You need to pay for it every year.
Please see here for more info: https://www.nextscripts.com/snap-plugin-vs-snap-api-difference/