Issues with SettingsGroups

Hello, not sure if it's me misunderstanding how they work, but I'm having issues with getting settingsGroups to work.

I place something akin to this

name: TestProj
settingsGroups:
  watchOS:
    base:
      TARGETED_DEVICE_FAMILY: 4
      WATCHOS_DEPLOYMENT_TARGET: 4.0
  iOS:
    base:
      IPHONEOS_DEPLOYMENT_TARGET: 11.0
options:
  createIntermediateGroups: true
  defaultConfig: Debug
  groupSortPosition: bottom
  transitivelyLinkDependencies: false
targets:
  appLib:
    platform: [iOS, watchOS]
    platformSuffix: "${platform}"
    productName: "appLib${platform}"
    settings:
      groups:
        - "${project}"
      configs:
        ENABLE_BITCODE: YES
    sources:
    - path: appLib/Test.swift
    - path: appLib/Test2.swift
    type: framework

But on running xcodegen, I always get - Invalid settings group "${project}"

Use the supplied YAML as the reproduction case and run xcodegen to confirm the invalid settings group error. Trace how settingsGroups and the ${project} group reference are validated, then verify the expected behavior or syntax against the resulting generated project and error message.