Post to Medium broken if using custom domain

The Post to Medium action does not work if you are using a custom domain for your URL on Medium.

If using the standard account setup with Medium where your URL is a subdomain like then the action works just fine.

With a custom URL like which points to Medium, this action does not work.

If anyone has any ideas for how to make this work, I’d be grateful.

Thanks in advance for any help you can offer.