Need help to setting up Social (NC 20.0.0, Social 0.3.1)

I’m running a Nextcloud instance in openSUSE Leap 15.2 (nextcloud-20.0.0-lp152.114.1.noarch, Social 0.3.1).

Hint: FQDN.FOO ist just a placeholder for the real server name.

# sudo -u wwwrun php /srv/www/htdocs/nextcloud/occ social:reset
Beware, this operation will delete all content from the Social App.

Do you confirm this operation? (y/N) y
Operation is destructive. Are you sure about this? (y/N) y

flushing data... done

Now is a good time to change the base address of your cloud:  (https://FQDN.FOO) 

# sudo -u wwwrun php /srv/www/htdocs/nextcloud/occ social:check:install
- 0 invalid followers removed
- 0 invalid notes removed

- Your current configuration: 
    "cloud_url": "https:\/\/FQDN.FOO\/",
    "social_url": "https:\/\/FQDN.FOOg\/index.php\/apps\/social\/",
    "social_address": "",
    "service": 1,
    "max_size": 10,
    "access_type": "all_but",
    "access_list": "[]"

Now I open and click “Follow”. After input zone42@FQDN.FOO and Continue, the login screen of my Nextcloud instance comes up, and I log in. Then the progress circle is rotating endlessly. :slightly_frowning_face:

What’s wrong here? How can I analyze what is going wrong?