get-rates-with-shipment-details/types/public-params.d.ts
declare type BillToAccount = "bill_to_country_code" | "bill_to_party" | "bill_to_postal_code";
In the example request here the following payload is used
"advanced_options": {
"bill_to_account": "123456789",
"bill_to_country_code": "US",
"bill_to_party": "third_party",
"bill_to_postal_code": "78756"
}
which if the type was accurate I wouldn't expect bill_to_account: "123456789" to be a valid rate request.