How specify ECS clusters?

Traefik Traefik v2 (latest)
1

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:
--providers.ecs.clusters=dev-cluster_r1

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": [
                "ecs:RunTask",
                "ecs:StartTask",
                "ecs:StopTask",
                "ecs:DescribeTasks",
                "ecs:ListTasks",
                "ecs:DescribeTaskDefinition",
                "ecs:ListTaskDefinitions"
            ],
            "Resource": [
                "arn:aws:ecs:us-east-1:xxx:task/*",
                "arn:aws:ecs:us-west-2:xxx:task/*",
                "arn:aws:ecs:us-east-1:xxx:task-definition/*",
                "arn:aws:ecs:us-west-2:xxx:task-definition/*"
            ]
        },

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
Thanks