GitLab pipelines pushes to remote server but cannot ssh - ssh

Question

My .gitlab-ci.yml looks like this:
build app:
stage: build
only:
- feature/ci-pipeline-job-v2
before_script:
- echo "before script"
- 'command -v ssh-agent >/dev/null || ( apt-get update -y && apt-get install openssh-client -y )'
- eval $(ssh-agent -s)
- echo "$SSH_PRIVATE_KEY" | ssh-add -
- mkdir -p ~/.ssh
- chmod 700 ~/.ssh
- echo "$GIT_URL" >> ~/.ssh/known_hosts
- chmod 644 ~/.ssh/known_hosts
- echo "HOST *" > ~/.ssh/config
- echo "StrictHostKeyChecking no" >> ~/.ssh/config
- git config user.email "user.villiers#main.com"
- git config user.name "user-main"
- git remote add acquia $GIT_URL
script:
- echo "running the script"
- git checkout -b feature/ci-pipeline-job-v2
- git push acquia feature/ci-pipeline-job-v2
after_script:
- echo "time to ssh"
- ssh maindecoupled.dev#maindecoupleddev.ssh.prod.acquia-sites.com "cd /var/www/html && ls -la && composer install && exit"
My pipeline gives a success, but when I look at the job result, I see a permission denied certainly from the after script.
The full result of the job is as follows:
$ echo "before script"
before script
$ command -v ssh-agent >/dev/null || ( apt-get update -y && apt-get install openssh-client -y )
$ eval $(ssh-agent -s)
Agent pid 12
$ echo "$SSH_PRIVATE_KEY" | ssh-add -
Identity added: (stdin) (userdevilliers#Norton-MacBook-Pro.local)
$ mkdir -p ~/.ssh
$ chmod 700 ~/.ssh
$ echo "$GIT_URL" >> ~/.ssh/known_hosts
$ chmod 644 ~/.ssh/known_hosts
$ echo "HOST *" > ~/.ssh/config
$ echo "StrictHostKeyChecking no" >> ~/.ssh/config
$ git config user.email "user.villiers#main.com"
$ git config user.name "user-main"
$ git remote add acquia $GIT_URL
$ echo "running the script"
running the script
$ git checkout -b feature/ci-pipeline-job-v2
Switched to a new branch 'feature/ci-pipeline-job-v2'
$ git push acquia feature/ci-pipeline-job-v2
Warning: Permanently added 'svn-23449.prod.hosting.acquia.com,22.222.22.222' (RSA) to the list of known hosts.
To svn-23449.prod.hosting.acquia.com:maindecoupled.git
b1f2c6ca..622cab3b feature/ci-pipeline-job-v2 -> feature/ci-pipeline-job-v2
Running after_script
00:02
Running after script...
$ echo "time to ssh"
time to ssh
$ ssh maindecoupled.dev#maindecoupleddev.ssh.prod.acquia-sites.com "cd /var/www/html && ls -la && composer install && exit"
Warning: Permanently added 'maindecoupleddev.ssh.prod.acquia-sites.com,11.11.111.111' (ECDSA) to the list of known hosts.
maindecoupled.dev#maindecoupleddev.ssh.prod.acquia-sites.com: Permission denied (publickey).
Cleaning up project directory and file based variables
00:01
Job succeeded
How am I able to push to the Acquia repo but have a public key error when its time to ssh?
Not sure how to go about from here.
How can I ssh into the remote server and cd into the intended directories?