Once you’ve completed the steps for CI Integration, set up Circle CI as follows: Step 1: Add the private key you created for the robot user to your Circle CI project through the Project Settings > SSH keys page on Circle CI. Step 2: Add a custom deploy step that pushes to Aptible following Circle’s deployment instructions. It should look something like this (adjust branch names as needed): 
deployment:
  production:
    branch: production
    commands:
      - git fetch --depth=1000000
      - git push git@beta.aptible.com:$ENVIRONMENT_HANDLE/$APP_HANDLE.git $CIRCLE_SHA1:master
📘 In the above example, git@beta.aptible.com:$ENVIRONMENT_HANDLE/$APP_HANDLE.git represents your App’s Git Remote.
Also, see My deploy failed with a git error referencing objects, trees, revisions or commits to understand why you need git fetch here.