Syncthing on docker swarm over raspbian: "Failed to create folder marker" error

Hello guys,

I’m trying to setup syncthing on a docker swarm set up accross two raspberry pis running the latest docker over raspbian. The setup works and I have portainer confirming all is fine.
I have deployed calibre web on that swarm and it works.

I’m trying to deploy syncthing to sync my calibre library from my laptop.
Syncthing starts but whenever I try to add a folder to sync, i get the following error message:

Failed to create folder marker: mkdir /calibredb/.stfolder: permission denied

i’m deploying the apps from portainer using stackdeploy.

Here is the full yml:

version: “3.7”

volumes:
calibredb:
external: true
config_calibre_web:
external: true
config_syncthing:
external: true

services:
calibre-web:
image: linuxserver/calibre-web
environment:
- TZ=Europe/Paris
- PUID=1000
- PGID=1000
volumes:
- config_calibre_web:/config
- calibredb:/books
ports:
- 8083:8083
deploy:
mode: replicated
replicas: 1

syncthing:
image: linuxserver/syncthing
environment:
- TZ=Europe/Paris
- PUID=1000
- PGID=995
- UMASK_SET=022
volumes:
- config_syncthing:/config
- calibredb:/calibredb
ports:
- 8384:8384
- 22000:22000
- 21027:21027/udp
deploy:
mode: replicated
replicas: 1

The volumes have been se up appart from portainer. They are docker volumes (not bind mounts).

Can someone tell me how come Syncthing doesn’t get access to the calibredb folder ?
Is this an ownership / acess right problem ?
How can I solve this ?

Many thanks