The Garo installation manual implies both the 'owner' and 'installer' need the app to complete the installation process. It seems to me that parameters such as charging current are likely set in the software, which points to an internet connection being necessary. The method of connection (wifi, ethernet, SIM) is part of installation planning, and setting up the connection is part of the install process.
It sounds maybe that the owner/installer steps (section 4.13) haven't been followed to get the Garo communicating with their server, so that the app can work?