It might be due to the platform's rules or a bug. Some platforms have specific rules about sharing others' stories. If it's not a rule issue, try logging out and logging back in. This can sometimes refresh the permissions and settings. If that doesn't work, contact the platform's support team. They can look into whether there's an issue with your account specifically or if it's a wider problem with the system.
Well, it could be that your friend has restricted the sharing options of their story. You should ask your friend to check their story settings. Additionally, there may be technical issues on the app side. For example, a poor network connection can sometimes cause problems when trying to add a story. Try switching to a better network, like from Wi - Fi to mobile data or vice versa, and see if that resolves the issue.