It could be that your account doesn't have the necessary permissions or your IGTV content doesn't meet the sharing criteria. Sometimes, it could also be a temporary issue with the platform.
It might be that the specific IGTV video you're trying to share has some restrictions or is not compatible with being shared on stories. Also, ensure your app is up to date as older versions might have sharing issues.
It could be that your account settings are not configured correctly for sharing. Check your privacy and sharing settings within the app. Also, make sure you have the latest version of the app installed as older versions might have this limitation.
It could be that the platform has certain restrictions or your account doesn't have the proper authorization. Also, make sure you're following the correct sharing steps.