I was so thankful to run across a mention about some app to help you cue for Notre Dame to avoid long wait times and basically book an appointment from nearby, but noticed there was limited info in the form and some questions. I took a few pics and am happy to answers questions as I was just there this past Saturday, October 14th
It worked perfectly, I was staying in Montparnasse and was able to be in range to book our appointment time.
Here is a photo of the sign posted above the appointment tickets machine encouraging you to download the app and what the appointment time ticket from the app looks like on your phone.
Hope this helps