Error / Task definition

[kamalkech]

{
  "family": FAMILY,
  "containerDefinitions": [
    {
      "image": "REPOSITORY_URI:BUILD_NUMBER",
      "name": NAME,
      "essential": true,
      "portMappings": [
        {
          "containerPort": 3000,
          "hostPort": 3000
        }
      ]
    }
  ],
  "cpu": "256",
  "memory": "512",
  "requiresCompatibilities": [
    "FARGATE"
  ],
  "networkMode": "awsvpc",
  "executionRoleArn": ROLE_ARN 
}

getting this error:
An error occurred (ClientException) when calling the DescribeTaskDefinition operation: Unable to describe task definition.
ROLE_ARN=

An error occurred (ClientException) when calling the DescribeTaskDefinition operation: Unable to describe task definition.
FAMILY=

An error occurred (ClientException) when calling the DescribeTaskDefinition operation: Unable to describe task definition.
NAME=