There could be several reasons. Maybe your account has some restrictions due to violating Instagram's rules. Another possibility is a technical glitch. Try restarting your device and the app. Also, check your internet connection as a weak or unstable connection can prevent you from sending messages on the story.
First, check your network. If it's poor, try switching to a better Wi - Fi or mobile data. Then, restart the Instagram app. Simple things like this often solve the problem.
It could be that your internet connection is unstable. Or, there might be some settings you need to check to enable message sending on the story feature.
Perhaps you don't have the proper permissions or your account has some sort of violation that's preventing you from sending messages. Another possibility is that the story feature is temporarily down for maintenance.
It depends. If a lot of users report the same problem at the same time, then it's likely a common issue related to Instagram itself, like a bug in the system or problems with the servers. However, if it's just you, it could be something specific to your device or account, such as a setting on your phone or a restriction on your account.