Well, to post longer videos on stories, you might need to upgrade your account to a premium version if the platform offers that. Also, check if your internet connection is stable as it can affect the upload process. Sometimes, splitting the long video into smaller segments and posting them consecutively is an option too.
First, make sure your app or platform supports longer video uploads. Then, check the size and format requirements. Usually, compressing the video to an appropriate size without losing much quality can help.
The key to posting longer videos on stories is to follow the platform's guidelines. Some platforms have specific settings or permissions for longer videos. It could also depend on your device and the version of the app you're using. Sometimes, clearing the app cache or reinstalling the app can solve upload issues.