How to scroll down or page down with Kantu?

I tried
XTYPE ${KEY_PAGE_DOWN}
on the page, but it’s not working

Make sure the browser has the focus. Here I use a very simply XClick (1,1) for it. It just clicks in the top right corner of the web page.

{
  "Name": "scrolldown",
  "CreationDate": "2019-7-18",
  "Commands": [
    {
      "Command": "open",
      "Target": "https://www.aliexpress.com/category/200001648/blouses-shirts.html",
      "Value": ""
    },
    {
      "Command": "XClick",
      "Target": "1,1",
      "Value": ""
    },
    {
      "Command": "XType",
      "Target": "${KEY_PAGE_DOWN}${KEY_PAGE_DOWN}${KEY_PAGE_DOWN}${KEY_PAGE_DOWN}",
      "Value": ""
    }
  ]
}

Just for completeness and as cross-reference: Other options are listed here: