Symptoms
When we try to delete subscription id 1234567, we get the following error
Cannot delete 1 subscription(s). Reason: {2}
Or
Cannot unsubscribe 1 subscriptions. Reason: Database db1234567_sa767676_main can not be changed or removed, it is used by site application #767676.
Cause
Failure occurs because the subscription contains site application Wordpress.
Resolution
Please remove the site application via CCP > Applications > Wordpress > domain.tld > Uninstall, wait for the tasks to complete, after that it will be possible to remove the subscription.