No Docker tag has been generated. Check tags input

I'm trying to use metadata-action@v5 along with docker/build-push-action@v6. Here's a portion of my workflow:

# ...
- name: Docker metadata
      id: metadata
      uses: docker/metadata-action@v5
      with:
        images: |
          ${{ steps.login-ecr.outputs.registry }}/${{ env.ECR_REPOSITORY }}
        tags: |
          type=schedule,pattern={{date 'YYYYMMDD-hhmmss' tz='Europe/London'}},enable=${{ github.ref_name != 'main' }}
          type=raw,value=latest,enable={{is_default_branch}}

    - name: Set up Docker Buildx
      uses: docker/setup-buildx-action@v3

    - name: Build, tag, and push image to Amazon ECR
      id: build-image
      uses: docker/build-push-action@v6
      with:
        context: .
        file: Dockerfile
        push: true
        tags: ${{ steps.metadata.outputs.tags }}
        cache-from: ${{ steps.login-ecr.outputs.registry }}/${{ env.ECR_REPOSITORY }}:latest
        build-args: BUILDKIT_INLINE_CACHE=1
        provenance: false
# ...

I intend to generate a timestamp tag for the Docker image when the workflow is run on a non-main branch, while using the latest tag when run on the default (main) branch

However, when I run the workflow for a non-main branch, the step build-image fails with the error:

ERROR: tag is needed when pushing to registry

Error: buildx failed with: ERROR: tag is needed when pushing to registry

I also see a couple of Warnings in the output of the metadata step, however can't make enough sense to spot the issue.

Processing images input
  name=xxxxxxxxx.dkr.ecr.eu-west-2.amazonaws.com/xxxxx/xxxxx,enable=true
Processing tags input
  type=schedule,pattern={{date 'YYYYMMDD-hhmmss' tz='Europe/London'}},enable=true,priority=1000
  type=raw,value=latest,enable={{is_default_branch}},priority=200
Processing flavor input

Warning: No Docker image version has been generated. Check tags input.
Warning: No Docker tag has been generated. Check tags input.

I can see that for the tag type=schedule, enabled is set to true which makes sense as I'm running the workflow for a non-main branch. However, the build-image step is not able to use the tag for some reason.

Two of your attributes are mutually exclusive. type=schedule is only available on the main branch. However, you specified

enable=${{ github.ref_name != 'main' }}

This is because type=schedule is meant for workflows triggered by a cron. Cron workflows only run on the main (or default) branch.