Facebook allows you to promote groups. Until recently, most ad accounts could choose a group as their objective for engagement.How to advertise group directly? Or , Do we have to do it via fanpage advertising?
Now, most accounts don't have this option. But it can be changed by api. This is just one parameter in your ad set. Later, when you add an ad. You will see the option to select the group.
You can also change it in the SoMe Planner app, somewhere I had a link to a video with instructions...