[6th Jul at 7:00pm EET] The issue was caused due to temporary downtime at Facebook side and has now been fixed. Let us know if you still experiencing problems. Thank you for your patience and sorry once again for the inconvenience.
[6th Jul at 7:00am EET] Seems like there is an issue at Facebook, which causes posts to Facebook Groups fail for some users. We are investigating the issue with Facebook and will update as more information comes available.
We are sorry for the inconvenience!