The main reason why auto approve may not be working is because you may be trying to post to a personal Facebook profile.  You cannot automatically post to Facebook personal profiles as it is against their terms and conditions.

See section Why Can't I Schedule Posts to My Personal Facebook Profile?

But fear not! We have created an elegant workaround. When it's time to share your post, our system will automatically notify you via email or push notification on your mobile app.

All you have to do is log in and push "Approved"!

Thankfully, this does not apply to Facebook Business Profiles, Twitter or LinkedIn.