How specify ECS clusters?

We have issues establishing ECS as the backend for Traefik in AWS.

Using version 2.3 RC we are specifying the cluster name in the container command like this:

and when trying to test we get this error

time="2020-08-13T20:12:31Z" level=debug msg="ECS Clusters: [dev-cluster_r1]" providerName=ecs
time="2020-08-13T20:12:32Z" level=error msg="Unable to list tasks" providerName=ecs
time="2020-08-13T20:12:32Z" level=error msg="Provider connection error AccessDeniedException: User: arn:aws:sts::xxxxxxx:assumed-role/xxxxxRole/xxxxxxx is not authorized to perform: ecs:ListTasks on resource: *, retrying in 17.242423998s" providerName=ecs

although our role has permissions defined like this:

            "Sid": "AllowECSTaskActions",
            "Effect": "Allow",
            "Action": [
            "Resource": [

Note : I used xxx to cover the real resources name
What is wrong here? We do not want to scan all clusters with *, so we are giving a cluster name dev-cluster_r1.
How do we have to define the clusters to be scanned in Traefik v2.3RC?
Any help welcome