Please be aware that it doesn't exist an official and supported way to recover deleted messages. This is a workaround and may encounter limitations caused by the selected messaging app or even the Android OS:
1) Text messages are recovered by your notifications, therefore, if you have put a chat on silence, or if you are currently watching a message on the messaging app before it's deleted you will not receive a notification so WAMR can't save it! This also obviously means that is impossible to recover notifications/messages before you downloaded this app (so download it quickly!).
2) If messages aren't being saved, it may be caused by Android killing WAMR. Please remove WAMR from all battery optimization services!
3) WAMR can't save files if they aren't completely downloaded! So if you are offline or you have an unstable connection, or in general if the sender deletes the message containing a media before the messaging app downloads it, WAMR can't do anything to save it.
4) If you aren't using a WiFi connection, some media may not be automatically downloaded by your messaging app because of your settings. You can change this behavior in Messaging app > Settings > Data and storage usage and increase your chances.
Other limitations may be caused by your Android version, or your system language (in particular if it is right-to-left). Please feel free to contact me and submit me any problem so I can try to fix it!