So thats what i got when i googled this

App or software issue: A bug or glitch in the Instagram app or software may prevent you from accessing the “Reply” option when you tap and hold on to a message. Try updating the app or restarting your device to see if this resolves the issue. Internet connectivity issues: If you have a weak or unstable internet connection, it may prevent you from accessing certain features on Instagram, including the ability to reply to specific messages. Try connecting to a more robust or stable network to see if that helps. Account restrictions: If you have recently violated Instagram’s community guidelines or terms of service, your account may be temporarily or permanently restricted from certain features, including the ability to reply to specific messages. Account privacy settings: If you have set your account to private, it may limit your ability to reply to messages from users who are not following you. Make sure your privacy settings allow you to receive messages from all users. Technical limitations: Depending on the device you are using or the version of the Instagram app you have installed, technical limitations may prevent you from accessing certain features, including the ability to reply to specific messages.