Hi
Under iOS 10.x, the Invisible Ink bubble effect can be applied to messages that are sent via Apple's iMessage service.
Whenever a message is sent with the Invisible Ink effect selected, in order to read that reply, the recipient needs to swipe the message bubble in order to reveal that reply's contents.
The message effect is only applied for any given reply if you specifically apply it using bubble effects.
More information and instructions:
Use message effects with iMessage on your iPhone, iPad, and iPod touch - Apple Support
http://help.apple.com/iphone/10/#/iph3d4cb79c9