"Unable to locate package php8.1" error when trying to install PHP in pipeline script

[Support]

So I'm trying to deploy a Wordpress plugin to a WPEngine-hosted website using Bitbucket Pipelines.

I'm using WPEngine's pipe: https://bitbucket.org/wpengine/wpe-site-deploy/src/main/pipe.yml 

I need to run "composer install" to install PHP dependencies before the pipe runs.

Here's my bitbucket-pipelines.yml:

pipelines:
  branches:
    master:
      - step:
        name: Deploy to Development
        script:

          - apt update && apt -y upgrade
          - apt -y install language-pack-en-base
          - export LC_ALL=en_US.UTF-8
          - export LANG=en_US.UTF-8
          - apt -y install software-properties-common
          - add-apt-repository --yes ppa:ondrej/php
          - apt update
          - apt -y install php8.1
          - curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
          - composer install
          - pipe: wpengine/wpe-site-deploy:v1
            variables:
              WPE_SSHG_KEY_PRIVATE: $WPE_SSHG_KEY_PRIVATE
              WPE_ENV: 'xxx'
              REMOTE_PATH: 'wp-content/plugins/xxx/'

Everything is running swimmingly until the part where it tries to install php8.1:

Reading state information...
E: Unable to locate package php8.1

But the repository was added without issues:

Above you can see successful adding of ppa:ondrej/php and apt update completed. But somehow it still can't find PHP 8.1

Can anyone help me out with this ?

[Support]

Answering my own question.

Turns out WPEngine by default already has Composer installed.

So I don't actually have to install and setup composer BEFORE their Pipe runs.

I can have a bash script in my source code which runs "composer install", and have this script run AFTER the pipe completes, like so:

pipelines:
  branches:
    master:
      - step:
          name: Deploy to Development
          script:
          - pipe: wpengine/wpe-site-deploy:v1
            variables:
              WPE_SSHG_KEY_PRIVATE: $WPE_SSHG_KEY_PRIVATE
              WPE_ENV: 'xxxx'
              REMOTE_PATH: 'wp-content/plugins/xxxx/'
              SCRIPT: 'bitbucket-pipelines-post-deploy.sh'