message: Change invoicePeriodStartDate to invoicePeriodEndDate for $filter
  $filter may be used to filter invoices by invoicePeriodEndDate, not by invoicePeriodStartDate. A customer copied the InvoiceExpand sample request from this doc: and got an error.
diff: "api-version": "2018-03-01-preview",
  "subscriptionId": "subid",
  "$top": 1,
  - "$filter": "invoicePeriodStartDate le 2017-02-01",
  + "$filter": "invoicePeriodEndDate le 2017-02-01",
  "$expand": "downloadUrl"
  },
  "responses": {
  