Pm2 Process or Namespace error with github action

I'm trying something for the first time with github action. I wrote a working system when I pushed anything. It successfully executes git pull and npm commands, but when I say pm2 restart app it gives an error like this.

err: [PM2][ERROR] Process or Namespace app not found

When I enter the server with terminal and make pm2 restart app it works successfully. The problem is only when I do it with github action.

My .yml file

name: Node.js CI

on:
  push:
    branches: [ master ]

jobs:
  deploy:
    runs-on: [ubuntu-latest]
    steps:
      - uses: actions/checkout@v1
      - name: Push to server
        uses: appleboy/ssh-action@master
        with:
          host: xxxx
          username: xxxx
          password:xxxx
          script: cd /root/www && npm run deploy && pm2 restart app