Verify your account permissions. Maybe your account has some limitations set that are preventing sharing. If it's a platform - specific issue, look for help on the official support page. There might be known issues and solutions related to sharing posts to stories that other users have already reported and had resolved.
Yes, there might be. Check if you have the correct permissions for sharing on the app. If not, enable them. Also, restart your device. Sometimes, a simple restart can solve glitches that prevent sharing.
It could be that your account settings are restricting the sharing feature. Check your privacy and sharing settings to make sure everything is enabled correctly.
It could be that your account settings are preventing the sharing. Check your privacy and sharing settings to make sure they allow sharing to your story. Also, make sure the post you want to share is allowed for such sharing.