Download all attachments from freshworks

I did an export of all data from freshworks, using the Export function from the GUI, in json. This zip includes CannedResponses.json, Companies*.json, Solutions.json, Tickets*.json, Users*.json. However, the attachments are not included in the zip file.
Tickets*.json has info about attachments. Some of the attachments listed have a attachment_url_for_export field, and some do not. Why is so?
How do I get all the attachments (programmatically using the API, or from the web)?

[
  {
    "helpdesk_ticket": {
      "id": ...
      "attachments": [
        {
          "id": ...,
          "content_file_name": ...,
          "content_content_type": "application/pdf",
		  # it does not contain a attachment_url_for_export nor attachment_url, why?
	...
  },
  {
    "helpdesk_ticket": {
      "id": ...
      "attachments": [],
      "notes": [
        {
          "id": ...,
		  "attachments": [
            {
              "id": ...,
              "content_file_name": ...,
              "content_content_type": "application/pdf",
              "attachment_url_for_export": "https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/.../original/...&X-Amz-Expires=604800",
              "attachment_url": null
            }
          ]
	...
  },