I fixed the problem. It was because of the mismatch of the user and group in the file /etc/systemd/system/traccar.service.d/run-as-user.conf. Later I fixed it.
But the google map was not working. I am trying to follow your discussion on https://www.traccar.org/forums/topic/google-map-layer/ based on the instruction https://www.traccar.org/map-layers/ .
Hopefully I will fix it
Thanks for your support and your contribution on open source.
Have you solved the problem?