As we can read here: https://support.goodnotes.com/hc/en-us/articles/7445581406095-Share-notebooks-between-iOS-and-other-platforms#share-notebooks-between-ios-and-other-platforms-0-0 the complete synchronisation between iOS App and Web Apps is not possible yet, but Link Sharing and editing should be working.
I just was testing the Link Sharing and editing option. The Sharing Option works, but the editing option does not synchronize between iOS App and WebApp.

Steps to reproduce:
1. Create Notebook on iOS App.
2. Create Share Link for that notebook in iOS App.
3. Open Link in Browser or Windows App.
4. Edit in Browser or Windows App.
5. Wait for Status "Synchronised" in Windows App.
6. Wait for Synchronisation in iOS App.
7. Does not Synchronize.
8. But does synchronize to a different Browser / Windows App.
OR:
4. Edit in iOS App.
5. Wait for Synchronisation.
6. Does not Synchronize to Windows App.

It would be a great benefit to be able to make that synchronisation work correctly.