Deploying Dockerised Scala Play App to Heroku

I am trying to deploy a docker container to heroku’s container registry which should be pretty straight forward. heroku requires the dockerfile to have a CMD command which sbt’s default

sbt docker:publishLocal

does not have but I am using this tutorial here which breaks is down pretty well but everytime i try to run my app in the docker container with the CMD command pointing to my default working directory (/opt/docker/bin/myapp) it gives me a

Bad root server path error: /opt/docker/bin/myapp

I followed the above tutorial to the letter and i think i am doing everything right. my docker file looks like so:

FROM openjdk:8-jre-alpine
WORKDIR /opt/docker
ADD --chown=daemon:daemon opt /opt
USER daemon
ENTRYPOINT ["/opt/docker/bin/myapp"]
CMD ["/opt/docker/bin/myapp"]
USER root
RUN ["apk", "add", "--no-cache", "bash"]

if anyone has any idea of how i can move past this and run my app using

docker run -p 5000:9000 myapp:1.0-SNAPSHOT

locally first (if it works locally, it will work on heroku) i would be eternally grateful.