Is it possible that you have multifactor turned on for Nextcloud?
If so, you can create a one-time password in your NC settings.
After backing up all my apps and their data, i updated my Lineage OS.
When i restored my Apps, it turned out that i had an CardDAV address book in use that was offline for a long time. Many contacts have been updated in the phone but never been synced. The problem is that i can’t re-establish the account within the new instance of Lineage, because the URL (and it’s server) is dead.
I had no success restoring Contacts, Contact Storage Provider (What does that by the way?), DAVdroid or Accounts.
[Q] How can i restore the contact data of the above mentioned CardDAV address book?
Updating a Samsung Galaxy S5 from Cyanogenmod 12 to Lineage 14.1 - using oandbackup and DAVdroid 1.9-ose
All contacts are stored in Androids contacts storage provider. If the sync did not run properly and your contacts storage is corrupt you can’t get your contacts back. I suggest to maybe look in the SQlite database directly. If you’ve a rooted phone as it seems you can access it also via adb. Look at our FAQ at point 3 and 4:
Maybe you can copy them from there or at least save it.
Also have a look here for a better understanding of the components involved with DAVdroid:
https://www.davdroid.com/faq/system-integration/ It always helps