Sorry to hear about the issues with duplicate messages using the Message+ app on your iPhone X. I can imagine how confusing it is to receive these duplicate messages and I'm happy to help figure this out. To clarify, are the duplicate messages being received only on the Message+ app are you are getting the messages both on the default (pre-installed) Messages app on your iPhone and the Message+ app? Is your operating system and the Message+ app up to date? You can check for an operating system update by going to settings, general, software update. You can update apps by opening the App Store and then selecting the updates tab and then "update".