AWS CodeBuild Batch configuration not passing environment variables

Question

I am trying to use the CodeBuild Batch configuration feature to trigger 2 different build from the same repository. For the 2 build commands, only some parameters differ which I am trying to manage through environment variables, below is the buildSpec file.

version: 0.2
batch:
  fast-fail: true
  build-list:
    - identifier: build1
      buildspec: buildspec1.yml
      env:
        variables:
          BUILD_ID:  build1ID
          privileged-mode: true
          PROJECT: Projectvalue
      ignore-failure: false
    - identifier: evaluator-build
      buildspec: buildspecs2.yml
      env:
        variables:
          BUILD_ID: build2ID
          PROJECT: ProjectValueTwo
      ignore-failure: false

phases:
  build:
    commands:
    - echo Build started on `date`
    - sbt clean
    - sbt 'project $PROJECT' 'compile'

Here Project is one of the variables I am trying to pass between the 2 builds, but the actual value is not being passed. I tried echoing the value for it but comes out as blank.

What could be wrong here? Also, is the batch config feature use correct here?