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Here is the search result Search results for 'facebook group post' - Make Community
If you peruse the search results, one of the result is Auto post to Facebook Groups from Facebook Page, which tells you that it is no longer possible to post into Facebook Groups via the API (automation).
For more information, see Due to the deprecation of the Facebook Groups API, we (Make) will be discontinuing our Facebook Groups app
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Did you know, the concepts of about 70% of questions asked on this forum are already covered in the Make Academy. Investing some effort into it will save you lots of time and frustration using Make later!