IAM role attachment issue to redshift cluster

I’m trying to attach and IAM role which is created already to a redshift cluster.
But I’m not getting any error in attaching. It does not attach the IAM role.

I’m using cluster_iam_roles = [complete arn], doesn’t work.
Also, i’m using

data “aws_iam_role” “iam” {
provider = “aws.test”
name = “NDH_Redshift_Role”

Then in my module. I’m calling -
cluster_iam_roles = “${data.aws_iam_role.iam.arn}”

But it doesn’t work. Can anyone suggest me, what i’m doing wrong.
I don’t get any error but attachment doesn’t happens.