Gitlab Pipelines Permission Denied (PublicKey)

I’m able to ssh into my droplet from my local machine. However, I have a gitlab pipelines job that fails to SSH to the production server at digital ocean. As far as I can tell, I’ve done everything correctly:

1. Copied public key into the production server’s ~/.ssh/authorized_keys
2. ran chmod -R go= ~/.ssh and chown -R $USER:$USER ~/.ssh as this guide suggests.
3. Copied private key into the PRODUCTION_PRIVATE_KEY variable in the CI/CD settings.

after running the job, it still fails when connecting to the server with the error code:

root@123.456.789.10: Permission denied (publickey).
ERROR: Job failed: exit code 1

Here’s my .gitlab-ci.yml:

before_script:
  - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )'
  - 'apt-get update -y && apt-get -y install rsync'
  - mkdir -p ~/.ssh
  - eval $(ssh-agent -s)
  - '[[ -f /.dockerenv ]] && echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config'

stage_deploy:
  artifacts:
    paths:
      - /
  #only run script when pushed to master branch 
  only:
    - master
  script:
    #get private key
    - ssh-add <(echo "$PRODUCTION_PRIVATE_KEY") 
    #make a _tmp directory on server **THIS IS WHERE IT FAILS**
    - ssh -p22 root@123.456.789.10 "mkdir /var/www/html/example.com_tmp"
    #copy all repo files to _tmp
    - rsync -avz --exclude=.git --exclude=src -r /builds/geochanto/example-wp/ george@123.456.789.10:/var/www/html/example.com_tmp
    #move site folder to _old, move _tmp to site
    - ssh -p22 j8rqv2sd9lt6@107.180.54.236 "mv /var/www/html/example.com/ /var/www/html/example.com_old && mv /var/www/html/example.com_tmp /var/www/html/example.com"
    #remove _old folder
    - ssh -p22 j8rqv2sd9lt6@107.180.54.236 "rm /var/www/html/example.com_old"