Apologies, but I've searched all the threads here (StackOverflow, etc), and while I've found lots of folks hitting it, I haven't found my solution. I set up a GitHub Action in my repo on push, essentially using the provided example on https://github.com/pandoc/pandoc-action-example.

I can run and access my input files fine with a simple run ls, via an /absolute/path, via ${{ github.workspace }}/path, or via $GITHUB_WORKSPACE/path so I know they are there.

But when I try to call pandoc with the yaml, I get the classic error:
pandoc: (my-valid/path): openBinaryFile: does not exist (No such file or directory)

My yaml:

on: push

jobs:
convert_via_pandoc:
    runs-on: ubuntu-18.04
    steps:
      # Checks-out repository under $GITHUB_WORKSPACE, so job can access it
      - uses: actions/checkout@v2
      - run: ls [valid/path].md
      - uses: docker://pandoc/core:2.11.2
        with:
          args: >- # break args into multiple lines
            -s
            -M title="My Title"
            -o output.html
            -f markdown
            [valid/path].md

Here's an example showing the path is valid, and the failure when I try to access that path as the input file (same occurs using $GITHUB_WORKSPACE, etc).

I am a newbie to both GitHub Actions and Pandoc, so it must be something obvious to the experts here. What am I doing wrong?

Thanks in advance.