Unable to find image 'xxxx' locally
Your project is being added to the image as /app. So, in the container, the project.json lives at /app/project.json. But your WORKDIR is set to /app/approot.
This effectively makes your ENTRYPOINT looking for project.json at /app/approot, which it does not exist. You'll either need to change WORKDIR to /app or COPY . /app/approot.