List contacts from connected provider (paginated, no import)

curl --request GET \
  --url https://api.sandbox.flowpayroll.ai/v1/billing/clients/provider-contacts \
  --header 'X-Auth-Token: <api-key>'

{
  "content": {
    "data": {
      "items": [
        {
          "providerId": "<string>",
          "name": "<string>",
          "emailAddress": "<string>",
          "taxNumber": "<string>",
          "companyNumber": "<string>"
        }
      ],
      "nextPageToken": "<string>"
    },
    "metadata": {
      "dateFormat": "<string>",
      "dateTimeFormat": "<string>"
    }
  },
  "metadata": {
    "dateFormat": "<string>",
    "dateTimeFormat": "<string>"
  },
  "errors": [
    {
      "field": "<string>",
      "reasonText": "<string>",
      "reasonId": "<string>",
      "reasonParameters": [
        {
          "key": "<string>",
          "value": "<string>"
        }
      ]
    }
  ],
  "message": {
    "text": "<string>",
    "textId": "<string>",
    "textParameters": [
      {
        "key": "<string>",
        "value": "<string>"
      }
    ]
  }
}