How do I use keywords with multiple brackets?

[plshelpidkwhatimdoing]

When I run gallery-dl with the -K switch, I sometimes see keywords with multiple brackets. For example gallery-dl -K https://civitai.com/models/153332/western-dragon-collection-xl-classic-style has

version['files'][N]['url']
  https://civitai-delivery-worker...

How do I add that to my conf file? Because everything I've tried so far failed, it just gave me "None". Here's how I'm trying to do it.

"civitai": {
    "metadata": "generation",
    "postprocessors": [
        {
            "name": "metadata",
            "event": "post",
            "filename": "{file[postTitle]}",
            "mode": "custom",
            "format": "{model[name]} : {version[files{url}]}\n\n\n{model[description]}"
        }
    ]
},

The {model[name]} and {model[description]} work as intended, but {version[files{url}]} (and {file[postTitle]} for some reason) don't work, they give "None". I've tried changing the type of bracket and even {version[files.N.url]} (and {version[files.url]}) but it still doesn't work. Gallery-dl itself doesn't give me any errors, even with -v enabled.

PS: What does the "N" mean?

[mikf]

version['files'] is a list of objects, with [N] being the index into that list (e.g. a Number). -K or standard format strings can't handle these very well, but you should be able to access the first item with version['files'][0]['url'].

The JSON output from -j is more useful here:

      "version": {
        "files": [
          {
            "hashes": [],
            "id": 130654,
            "metadata": {
              "format": "SafeTensor",
              "fp": null,
              "size": null
            },
            "modelVersionId": 171702,
            "name": "Classic Western Dragons XL.safetensors",
            "pickleScanMessage": "No Pickle imports",
            "pickleScanResult": "Success",
            "scannedAt": "2023-09-28T14:45:54.541Z",
            "sizeKB": 167426.91796875,
            "type": "Model",
            "url": "https://civitai-delivery-worker-prod-2023-09-01.5ac0637cfd0766c97916cefa3764fbdf.r2.cloudflarestorage.com/model/606136/classic20western.oYyG.safetensors",
            "virusScanMessage": null,
            "virusScanResult": "Success",
            "visibility": "Public"
          }
        ]
      }

[plshelpidkwhatimdoing]

version[files][0][url] worked, thank you.