First time setup - Folder access errors

I have recently tried to learn Linux from a long user of Veeam backup and Windows server. I’m running all my applications in Docker-Compose and I have some issues running Duplicacy in this application as well. I have a active license if that matters. I have search trough multiple forums included this one searching for some answers. I have been a bit lazy with my user access inside docker giving too much root access, I have anyway secured my Linux with settings from my firewall to disable access from the outside. When I try to add my Google .JSON file I can see I have only access to some folders in Linux with the Web GUI, for example /backup and /bin. The folder I want access to is /OPT, but is seems there is a access issue inside my cointainer, I get " no such file or directory" error message. Please let me know if I miss anything, do I have to add backup volume inside “volumes”?

My docker consist of this config file:
image: erichough/duplicacy
hostname: duplicacy-web
container_name: duplicacy_backup
restart: always
- 3875:3875
- USR_ID=1000
- GRP_ID=1000
- TZ=Europe/Berlin
- /opt/duplicacy/config:/etc/duplicacy
- /opt/duplicacy/cache:/var/cache/duplicacy
- /opt/duplicacy/storage:/storage

Yes, you need to map the folder to be backed up to a folder inside the docker (such as /backup) so that the docker can access the folder.

In addition, the container you are using has fixed duplicacy_web version 1.2.1 and fixed duplicacy CLI 2.4.0: Docker

These are, to put it mildly, old. I would run duplicacy directly (it does not benefit from containerization anyway) or use a different container.