Unexpected output in pull request notification

[IvanNoronha-TomTom]

I'm using the action with following parameters

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
      - name: Send PR details to slack for review
        env:
          SLACK_WEBHOOK_URL: ${{ secrets.MYCHANNEL }}
          PULL_REQUEST_NUMBER : ${{ github.event.pull_request.number }}
          PULL_REQUEST_TITLE : ${{ github.event.pull_request.title }}
          PULL_REQUEST_AUTHOR_NAME : ${{ github.event.pull_request.user.login }}
          PULL_REQUEST_AUTHOR_ICON_URL : ${{ github.event.pull_request.user.avatar_url }}
          PULL_REQUEST_URL : ${{ github.event.pull_request.html_url }}
          PULL_REQUEST_BODY : ${{ github.event.pull_request.body }}
          PULL_REQUEST_COMPARE_BRANCH_NAME : ${{ github.event.pull_request.head.ref }}
          PULL_REQUEST_BASE_BRANCH_NAME : ${{ github.event.pull_request.base.ref }}
          IS_SEND_HERE_MENTION : false
        uses: jun3453/slack-pr-open-notification-action@v1.0.3

The usual output is(few fields removed)

For some reason today it is

The pull request number was 15 but we do not have a private channel with just the name 15 or #15. Is there a way I can further debug this as to what value was sent to PULL_REQUEST_NUMBER ?