iOS 8.x adds an important feature to the Lockscreen notifications – Quick Reply. With this, you'll be able to reply to messages, mark email as read, favorite tweets and do much more instantly from the lockscreen itself.
One of the most interesting use-case is the Message app. When you get a message from a friend, you can reply instantly from the lockscreen (without having to unlock screen, open the app and reply in the thread). However, many users have reported that the quick reply feature isn't working on their iPhones (notably, iPhone 5). Here are some fixes you should try:
How to Fix Quick Reply not Working on iPhone Running iOS 8
Solution #1: One of the simplest things about Quick Reply from lockscreen (for Messages) is the fact that you can reply only if you know what the message is. If, for some reason, you have disabled Message previews (privacy mostly), you won’t be able to see any options for quick reply on the lockscreen. That’s obvious because you can’t ‘quick reply’ to a message whose content you don’t know about.
To turn on message previews (it's usually enabled by default):
- Open Settings
- Tap on Notifications
- Next, tap on Messages
- Turn on the switch for Show Preview
Solution #2: A small setting in Passcode can also prevent “quick reply” features from showing up. This one's hidden inside your Passcode (TouchID & Passcode on iPhone 5s and later) setting.
- Open Settings
- Tap on Touch ID & Passcode (or Passcode on iPhone 5 and 4s)
- Scroll down and under Allow Access When Locked enabled Reply with Message
This is again obvious. If you use a passcode, that means you want to prevent someone from being able to “quick reply.” However, if you’re sure that no one else will be accessing your iPhone, you can enable Reply With Message so that you can quickly reply.
If these things fail to fix the problem, you might try resetting your iPhone.