This one works

Working IoT Policy.json

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "iot:Connect"
      ],
      "Resource": [
        "*"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Publish"
      ],
      "Resource": [
        "arn:aws:iot:us-east-1:123456789012:topic/my_org/my_grp/my_scope"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Subscribe",
        "iot:Receive"
      ],
      "Resource": [
        "arn:aws:iot:us-east-1:123456789012:topic/my_org/my_grp/my_scope",
        "arn:aws:iot:us-east-1:123456789012:topicfilter/my_org/my_grp/my_scope/*"
      ]
    }
  ]
}