[17th of Oct 7am EET] It seems like Meta has fixed the issue, and Facebook and Instagram Story posting should now work normally. We are still monitoring the situation and will provide updates if anything changes. Sorry once again for the inconvenience.
[16th of Oct 1pm EET] Meta is currently experiencing issues affecting Facebook and Instagram Story posts, causing some to fail. We are investigating this with Meta and will provide updates as soon as possible.
We apologize for the inconvenience!