Iam User for Billing

By the way, the namespace "aws-portal" is obsolete, so there is a high possibility that it cannot be used. https://docs.aws.amazon.com/cost-management/latest/userguide/billing-permissions-ref.html

To allow all billing-related operations, you will need the following policies:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "tax:*",
                "billing:*",
                "invoicing:*",
                "ce:*",
                "budgets:*"
            ],
            "Resource": "*"
        }
    ]
}

Alternatively, it may be easier to set a policy called "Billing" in the AWS Managed Policy for your IAM user. https://docs.aws.amazon.com/aws-managed-policy/latest/reference/Billing.html