I had this issue deploying a node app to Azure App Services.

I fixed it by adding a zip and an unzip step.

zip step is

  - name: Zip artifact for deployment
    run: zip release.zip ./* -r

unzip step is

  - name: unzip artifact for deployment
    run: unzip release.zip

Add the zip step after the build step and before Upload artifact step like this

  - name: npm install, build, and test
    run: |
      npm install
      npm run build --if-present
      npm run test --if-present

  - name: Zip artifact for deployment
    run: zip release.zip ./* -r

  - name: Upload artifact for deployment job
    uses: actions/upload-artifact@v2
    with:
      name: node-app
      path: release.zip

Then the unzip step is added after the download artifact step and before the deploy step like this.

steps:
  - name: Download artifact from build job
    uses: actions/download-artifact@v2
    with:
      name: node-app
      
  - name: unzip artifact for deployment
    run: unzip release.zip

  - name: 'Deploy to Azure Web App'
    id: deploy-to-webapp
    uses: azure/webapps-deploy@v2
    with:

I also faced this issue when deploying a react based app to Azure App service.

To add to the answer written by @steve, If the App service instance is windows based, one can use Powershell's Compress-Archive.

In build steps - zipping

Compress-Archive . release.zip

In deploy steps - unzipping

Expand-Archive release.zip

or

unzip release.zip

if the deployment script is using bash

You can zip all the files using below command and then upload the zip folder as your artifacts.

zip artifact.zip <generated_files>/*