val smartReply = FirebaseNaturalLanguage.getInstance().smartReply
smartReply.suggestReplies(conversation)
    .addOnSuccessListener { result ->
        if (result.status == STATUS_SUCCESS) {
            val ri = RemoteInput.Builder(...)
                .setChoices(result.suggestions)
                .build()
            notificationActionBuilder.addRemoteOnput(ri)
            ...
        }
    }}

// 1. pass conversation text to Smart Reply to suggest
//    and it will return suggestions to the callback
// 2. take the suggestions and set them on your notifications remote input