Can't delete files

[dongennl]

Hi, I'm probably missing something obvious but I can't get my files deleted; everything else works. (arc 0.11.0; arc_gcs 0.2.3)

Here's my uploader

defmodule Forluxury.Image do
  use Arc.Definition
  use Arc.Ecto.Definition

  @versions [:original, :thumb]
  @acl :public_read

  def transform(:thumb, _) do
    {:convert, "-resize 75x75 -background white -gravity center -extent 75x75"}
  end

  def transform(:original, _) do
    {:convert, "-resize 350x350 -background white -gravity center -extent 350x350"}
  end

  def filename(version, _) do
    version
  end

  def storage_dir(_version, {_file, scope}) do
    if scope do
      "images/#{scope.auction_id}/#{scope.image_uuid}"
    end
  end

  def __storage, do: Arc.Storage.GCS

  def gcs_object_headers(_, {file, _scope}) do
    [content_type: MIME.from_path(file.file_name)]
  end
end

the fields auction_id & image_uuid exist in the db and are populated (the generated URLs are correct); I don't delete the db record before trying to delete the file.

in iex:

path = Forluxury.Image.url({img.image, img}, :thumb)
"https://storage.googleapis.com/ddd-images-dev/images/6b00f8c4-805b-4c7d-be4a-b3c34f60e7f8/e59279d8-37b1-11eb-aaa3-7c6d628fbb76/thumb.JPG?v=63774471479"
Image.delete({path, img})
:ok

I'm not sure what I'm missing, but it just ignores the delete. I've also tried removing the "?v=xxxx" bit, same result. Same for the 'original' version or no version specified.
My service account has "Storage Object Admin" and "Storage Object Creator" permissions.

Any pointers greatly appreciated or how I could further diagnose this. I'm not sure what else to try.