The paper format is not configured in the Magento extension, but in the DHL Business Customer Portal (Geschäftskundenportal). Please note: by default, the printer settings do not apply globally, but on a per-user-basis.
Follow this procedure to configure the printer settings for all users:
- Log in to the Business Customer Portal as master user.
- At the top, select "All users".
- Configure the printer settings as desired. The settings will now apply to all users, which includes the special system user in the Magento configuration.