Let's Encrypt SSL Certificate Cannot be Used

To me this sounds like something wrong with docker mounted volumes.

Dockers cannot access each others files/folders by nature.
This means, you have to mount a volume on the host on both dockers, so they can both access it.

Or, you could use another way; on my previous (W10) setup I used the Samba add-on to gain access to my SSL certificates on HA (running on VMWare), which also worked fine

What do you mean by “both dockers?” I only have the docker container for my HA. Also, HA on Docker doesn’t have add-ons, so your method doesn’t seem to be an option from my understanding.

I tried creating and mounting a volume with the letsencrypt path. It still didn’t work. I got the same error as before. I added the following to the bottom of my docker-compose. It is at the same indentation level as services (which is to say it is not indented at all). It composes and mounts as expected. I can even read the contents of the file from the command line as I could before.

volumes:
  ssl_vol:
    driver: local
    driver_opts:
       o: bind
       type: none
       device: /private/etc/letsencrypt

How might I give the user permission?

I’d start by checking that you’re using the official HA image, and not the LSIO one.

Then open a shell in the container and check you can read both certificates using the path listed in configuration.yaml