This is my yml file:

name: Deployment M1 Develop

on:
  push:
    branches:
      - develop
    paths:
      - 'src/8.2/**'
      - '.github/workflows/deploy_dev.yml'

jobs:
  build:
    runs-on: ubuntu-latest
    container: openmage/php:8.2.18
    steps:
      - name: Checkout
        uses: actions/checkout@v2

      - name: Run composer install
        run: composer install

      - name: Install rsync and openssh-client
        run: |
          apt-get update
          apt-get install -y rsync openssh-client

      - name: Install SSH Key
        uses: shimataro/ssh-key-action@v2
        with:
          key: ${{ secrets.PIPELINE }}
          known_hosts: unnecessary

      - name: Create SSH directory
        run: mkdir -p ~/.ssh

      - name: Adding Known Hosts
        run: ssh-keyscan -H ${{ secrets.SSH_HOST }} >> ~/.ssh/known_hosts

      - name: Rsync files to remote server
        run: |
          rsync -avz --exclude-from excludes.txt --delete ./* ${{ secrets.SSH_USER }}@${{ secrets.SSH_HOST }}:/var/www/html/

      - name: Execute deploy.sh on remote server
        run: ssh -o StrictHostKeyChecking=no ${{ secrets.SSH_USER }}@${{ secrets.SSH_HOST }} 'bash -s' < /var/www/html/.github/deploy_dev.sh

THE PIPELINE variable contains the private key content. Not sure what am I doing wrong here, but i still receiving this error:

Host key verification failed.
rsync: connection unexpectedly closed (0 bytes received so far) [sender]
rsync error: unexplained error (code 255) at io.c(231) [sender=3.2.7]
Error: Process completed with exit code 255.

Any clue or help is appreciated. Thanks!