Owncloud 9.1.0 error cron job, config and apps folder not writable

Updated from an older ownCloud 7 and 8 earlier):

Steps to reproduce
1. Debian Jessie, Nginx, PHP 7.0, MySQL (up-to-date)
2. User webserver changed from www-data to X (id=900). Made member of group www-data
3. User php changed to X
4. Permissions www and subfolders set to Owner=X and Group=www-data (755 for dirs and 664 files)
5. Cron job made for user X (sudo crontab -e -u X -l and the added
*/15 * * * * php -f /var/www/owncloud/cron.php)
6. In Owncloud/config.php a line:
'overwrtite.cli.url'=> 'https://mfullyqualifiedsitename',

Expected behaviour
Owncloud should function without error in admin screen.

Actual behaviour
Error in admin screen says that config folder and apps folder are not writable. Cron error also. The given link (a ref....) is wrong because it refers to a doc page)

Research and Solution
After hours of searching and no relevant errors in logs I concluded that Owncloud may use a wrong path for Cron CLI job.

Removing the line:
'overwrtite.cli.url'=> 'https://mfullyqualifiedsitename',
from the config.php
made all errors go away!

I saw that this issue occurs more often. That is why I share this inf.