When accessing Github Marketplace Actions I am seeing getting error: should be either '[path]/Dockerfile' or 'docker://image[:tag]'

Question

My requirement is to create a public repo and make it available as an Action on Github Marketplace (already done). I am trying to understand the reason for the below error. There are 3 repos that I am referring to:

1. Private repo (with a public image) - deployed on ghcr.io
2. Public repo that accesses the public image of private repo in number 1 - This is a Marketplace Action
3. Public repo outside the org to try testing the repo in number 2

Summary The action.yml in the public repo (number 2) will access a public image of the private repo.

1  name: My Action
2  description: My GitHub Action Details
3  author: 36f
4  branding:
5    icon: activity
6    color: blue
7      
8  inputs:
9    input_name:
10   description: URL
11   required: true
12   default: 'https://url.com' 
13
14 runs: 
15   using: 'docker'
16   image: 'ghcr.io/repository/image_name:main' - i tried this
# image: 'repository/image_name:main' - i also tried this & got the same error

Line 15 and 16 is where I am having trouble

Now, when I try to access the image from outside the org (number 3), i use this snippet in the actions.yml file which is under .github/workflows folder

- name: My Action
  uses: public-repo/image_name@v1
    with:
      url: 'https://url.com'

When the Action is triggered, I get this error about the image:

should be either '[path]/Dockerfile' or 'docker://image[:tag]'.

What 'value' should I use for the using key (line 15) that will accept ghcr.io? Are there other recommendations how to do this?

If more info is needed please let me know.