unable to get credentials and initialize API ... read /home/opuser/.op/1password-credentials.json:

In the Docker Compose example config that we've published, we're using the Docker Compose feature to specify files as volumes (i.e. the 1password-credentials.json file). There's a small downside of that approach though, and is that if the file is not present or can't be found for whatever reason, Docker Compose won't fail, but will just continue and interpret the specified file as a directory instead.

So you'll have to make sure the 1password-credentials.json file is in the very same directory where you're running docker-compose up from. (And I don't see anything in your script around the credentials file, but maybe that's in the part you left out?)