Currently, you cannot follow a Pinterest Group.
What's the difference?
Pinterest Board URLs look like this: www.pinterest.com/Group-Name/Board-Name/
Pinterest Group URLs look like this: www.pinterest.com/Group-Name/
When setting up your POWR feed, make sure to include the group AND board, like the examples seen here.
Here are some other examples of Pinterest Boards which you can add to your POWR Feed: