Use powershell script to customize azure devOps pipeline?

I have an azure function app that is running on Azure. I am now trying to configure the application based on a powershell script. This powershell script is being used to create azure resources (Ex: KeyVault, ApplicationInsights...) that will be then used by the function app. I created the powershell script and my question here is how can I add the powershell script in the yaml file which is responsible to deploy the application. The powershell script is located in the repository under the name functionapp.ps1 . The idea here is to run the powershell script once the build is finished so in the deploy stage. What I did so far is the following:

 stages:
 - stage: Build
   displayName: Build stage
    
   jobs:
   - job: Build
     displayName: Build
     pool:
       vmImage: $(vmImageName)
    
     steps:
     - task: DotNetCoreCLI@2
       displayName: Build
       inputs:
         command: 'build'
         projects: |
           $(workingDirectory)/*.csproj
         arguments: --output $(System.DefaultWorkingDirectory)/publish_output --configuration Release
    
     - task: ArchiveFiles@2
       displayName: 'Archive files'
       inputs:
         rootFolderOrFile: '$(System.DefaultWorkingDirectory)/publish_output'
         includeRootFolder: false
         archiveType: zip
         archiveFile: $(Build.ArtifactStagingDirectory)/$(Build.BuildId).zip
         replaceExistingArchive: true
    
     - publish: $(Build.ArtifactStagingDirectory)/$(Build.BuildId).zip
       artifact: drop
    
 - stage: Deploy
   displayName: Deploy stage
   dependsOn: Build
   condition: succeeded()
    
   jobs:
   - deployment: Deploy
     displayName: Deploy
     environment: 'development'
     pool:
       vmImage: $(vmImageName)
    
     strategy:
       runOnce:
         deploy:
    
           steps:
           - task: CmdLine@2
             inputs:
               script: |
                 echo  '$(System.DefaultWorkingDirectory)'
                 dir
                    
           - task: PowerShell@2
             inputs:
               targetType: 'filePath'
               filePath: $(System.DefaultWorkingDirectory)/functionapp.ps1
    
           - task: AzureFunctionApp@1
             displayName: 'Azure functions app deploy'
             inputs:
               azureSubscription: '$(azureSubscription)'
               appType: functionApp
               appName: $(functionAppName)
               package: '$(Pipeline.Workspace)/drop/$(Build.BuildId).zip'

When the stages are being run and it arrives to this task I get the following error:

##[error]Invalid file path 'D:\a\1\s\functionapp.ps1'. A path to a .ps1 file is required.

I tried using the command line task to check the default working directory and I got the following result: D:\a\1\s

I still don't know what I am missing here and why I am getting this error. Can someone please give me a concrete solution to this problem ?

I ended up having the same error. Can someone please tell me what is the issue here ?