Quick replies does not work with all apps. I can quick reply to Instagram and Facebook messages on Android. This feature is not available currently on iOS according to the manual. I suspect Apple would have to open up something in their apps to allow this. Apple is very reluctant to allow their apps to communicate with other, non-Apple devices (Walled Garden).
Sorry @bob_ this is a limitation that Fitbit is not in control of.
Apple in their wisdom to have full control over the users experience wants the users to use their products and apps. Apple has therefore blocked all this party apps from being able too respond to notifications out side of their app.
This also goes for all of Fitbit competitors, other than the AW.