Function deployment fails if functions folder not in project root

[depdg]

My functions folder is on level /apps/myapp/functions instead of just /functions.
Also firebase.json is on level /apps/myapp.

Deploying function with PROJECT_PATH set still failes.

- name: Deploy Firebase
uses: w9jds/firebase-action@master
with:
args: deploy --only functions
env:
GCP_SA_KEY: ${{ secrets.GOOGLE_CREDENTIALS_BASE64 }}
PROJECT_ID: ${{ vars.FIREBASE_PROJECT_ID }}
PROJECT_PATH: ${{ github.workspace }}/apps/myapp

GitHub Action log:
i deploying functions
Running command: npm --prefix "$RESOURCE_DIR" run build
npm error code ENOENT
npm error syscall open
npm error path /github/workspace/functions/package.json
npm error errno -2
npm error enoent Could not read package.json: Error: ENOENT: no such file or directory, open '/github/workspace/functions/package.json'

The debug log shows it actually runs this, where workdir is set to "/github/workspace":
/usr/bin/docker run --name w9jdsfirebaseactionv14140_b2e680 --label 4a74bc --workdir /github/workspace --rm -e "GCP_SA_KEY" -e "PROJECT_ID" -e "PROJECT_PATH" -e "INPUT_ARGS" -e "HOME" -e "GITHUB_JOB" -e "GITHUB_REF" -e "GITHUB_SHA" -e "GITHUB_REPOSITORY" -e "GITHUB_REPOSITORY_OWNER" -e "GITHUB_REPOSITORY_OWNER_ID" -e "GITHUB_RUN_ID" -e "GITHUB_RUN_NUMBER" -e "GITHUB_RETENTION_DAYS" -e "GITHUB_RUN_ATTEMPT" -e "GITHUB_ACTOR_ID" -e "GITHUB_ACTOR" -e "GITHUB_WORKFLOW" -e "GITHUB_HEAD_REF" -e "GITHUB_BASE_REF" -e "GITHUB_EVENT_NAME" -e "GITHUB_SERVER_URL" -e "GITHUB_API_URL" -e "GITHUB_GRAPHQL_URL" -e "GITHUB_REF_NAME" -e "GITHUB_REF_PROTECTED" -e "GITHUB_REF_TYPE" -e "GITHUB_WORKFLOW_REF" -e "GITHUB_WORKFLOW_SHA" -e "GITHUB_REPOSITORY_ID" -e "GITHUB_TRIGGERING_ACTOR" -e "GITHUB_WORKSPACE" -e "GITHUB_ACTION" -e "GITHUB_EVENT_PATH" -e "GITHUB_ACTION_REPOSITORY" -e "GITHUB_ACTION_REF" -e "GITHUB_PATH" -e "GITHUB_ENV" -e "GITHUB_STEP_SUMMARY" -e "GITHUB_STATE" -e "GITHUB_OUTPUT" -e "RUNNER_OS" -e "RUNNER_A

Another repo where the functions folder is on root works just fine.
Is that a bug or does anyone spot the error I made in my CI?