You mean this MIT tutorial
https://appinventor.mit.edu/explore/ai2/piccall.html
When I scan the QR code to download the app, the app downloads and installs.
What link are you using to get the PicCall app example Carolyn?
(You can also download the source code (the aia) and work with it in the App Inventor compiler).
Try the above link. If the download does not load, it might be because of Warning: PicCall does not work on all Android phones in the current implementation of App Inventor: you'll get an error notice on some phones when you try to pick a phone number. Also, you won't see all your contacts — only those created from Gmail. These limitations will be removed in the future.
Is that the notice you are referencing?
What Android version and phone do you have Carolyn? This won't work if you are using an emulator or a Tablet that does not have a network connection.
Does this help?
Regards,
Steve