Two things are missing here:
- Swarm mode not enabled https://docs.traefik.io/v2.0/providers/docker/#swarmmode
- Service port not specified (it's mandatory for swarm) https://docs.traefik.io/v2.0/routing/providers/docker/#services
Regarding point two, for the dashboard/api you need to create a dummy service and put some port on it. An example is here