If you get the error message "Please enter a Folder ID or a valid Folder URL" in Folder Copy app
or Folder Notification app
it is may be you entered an url not recognized by the app. Below you can find 2 ways to get the ID of your Google Drive folder.
In the address bar
It is the last ID of the address bar.
By using the get link menu
On your drive right click on a folder and click on get link
You get an url like this : https://drive.google.com/open?id=ID_OF_THE_GOOGLE_FOLDER&authuser=0
You can copy/paste directly this url or just the ID.