in fact, i have read the guide and installed all the  external python dependencies : dropbox, nextcloud , nextcloud-api-wrapper , boto3 and paramiko but nextcloud, because there is no a lib named 'nextcloud' exactly.

dalec-nextcloud

django-nextcloud-storage

gitlab2nextclouddeck

hausschrat-nextcloud-s3

nextcloud-api-wrapper

nextcloud-async

nextcloud-deck

nextcloud-notes-ap

nextcloud-orm

nextcloud-sdk

nextcloud-status

nextcloud-talk-recording

nextcloud-tasks-api

nextcloud news filter

nextcloud news updater

nextcloudmonitor

nextcloudtalkbot

nextcloudtasks

pibooth-nextcloud

python3-cyberfusion-nextcloud-support

1. You have to make sure that there is .py file which has text _name = 'db.backup.configure' and _name = 'dropbox.auth.code'
2. then check file __init__.py inside models folder. make sure the file names on point 1 is included there in text from . import {filename}
3. last, check __init__.py outside folder models. make sure it has text from . import models

If all points above were checked and the error still happen, check on module dependencies. You might install module that depend to another modul which you not owned​

The security csv file is being processed and raise error suggest module was in correct path and added. The model was not available suggest python was stopped somewhere. So there must be more python error.

The main culprit maybe you think backup is just another module and you install it the way you do with most other business related module and do not read the Readme file or installation guide. Normally some other python packages will need to be installed such as paramiko. Make sure you pay a visit to the readme