AWS CodeBuild Error with Docker Runtime Version from Parameter Store

Question

I am encountering an issue with AWS CodeBuild when trying to specify the Docker runtime version using AWS Systems Manager Parameter Store. I am hoping to get some insights or solutions from those who might have faced a similar problem.

Here's the snippet of my buildspec.yml:

version: 0.2
env:
  parameter-store:
    DOCKER_VERSION: docker-version
phases:
  install:
    runtime-versions:
      docker: $DOCKER_VERSION

I have defined docker-version in AWS SSM Parameter Store with the value '20'. When I trigger the build, it fails at the build stage with the following error:

Phase context status code: YAML_FILE_ERROR Message: Unknown runtime version named '**.10.24' of docker. This build image has the following versions: **

Interestingly, when I specified the Docker version via variables in the buildspec.yml like so:

version: 0.2
env:
  variables:
    DOCKER_VERSION: 20
phases:
  install:
    runtime-versions:
      docker: $DOCKER_VERSION

It works without any issues. The following also worked:

version: 0.2
env:
  parameter-store:
    RUBY_VERSION: ruby-version #defined in Parameter Store with the value '3.1'
phases:
  install:
    runtime-versions:
      ruby: $RUBY_VERSION

Is there a known issue with referencing Docker versions from the Parameter Store in AWS CodeBuild's buildspec.yml? Any advice or insights would be greatly appreciated. Thank you in advance for your help!