Azure Build Pipeline cannot locate a file in dotnet core project

I have a PowerShell script in a folder in the source code for my project. I am trying to execute the file to make a third party call at the end of my build pipeline. When I look at the source repo the file is in the following folder:

ProjectName\Scripts\pwsh\PowerShell1.ps1

The build pipeline has the following task:

- task: PowerShell@2
  displayName: Third Party Call
  inputs: 
    filePath: '$(Build.SourcesDirectory)\ProjectName\Scripts\pwsh\PowerShell1.ps1'
  pwsh: true

I get the following error:

##[error]Invalid file path 'D:\a\s\ProjectName\scripts\pwsh\PowerShell1.ps1'. A path to a .ps1 file is required.

It is my understanding that $(Build.SourcesDirectory) is the root directory of the source of the project, so I assumed it would have the same folder structure as my repo. I don't know where to go from here as I can't see what is in $(Build.SourcesDirectory) to alter the file path to the correct location of my PowerShell script. Can someone advise me where I need to point please?

Edit: full yml file for the pipeline.

trigger:
- master

pool:
  vmImage: 'windows-latest'

variables:
  solution: '**/*.sln'
  buildPlatform: 'Any CPU'
  buildConfiguration: 'Release'

steps:
- task: UseDotNet@2
  displayName: 'Use dotnet 7'
  inputs:
    version: '7.0.x'
    packageType: runtime

- task: DotNetCoreCLI@2
  inputs:
    command: 'publish'
    publishWebProjects: true
    arguments: '--configuration $(buildConfiguration) --output $(Build.ArtifactStagingDirectory)'

- task: VSBuild@1
  inputs:
    solution: '$(solution)'
    platform: '$(buildPlatform)'
    configuration: 'DatabaseBuild'
    maximumCpuCount: true
    msbuildArchitecture: 'x64'

- task: CopyFiles@2
  inputs:
    SourceFolder: '$(System.DefaultWorkingDirectory)'
    Contents: |
      **/*.dacpac
    TargetFolder: '$(Build.ArtifactStagingDirectory)'

- task: PublishBuildArtifacts@1
  inputs:
    PathtoPublish: '$(Build.ArtifactStagingDirectory)'
    ArtifactName: 'drop'
    publishLocation: 'Container'

- task: PowerShell@2
  displayName: New Relic Deployment Marker
  inputs: 
    filePath: '$(Build.SourcesDirectory)\ProjectName\scripts\pwsh\PowerShell1.ps1'
    arguments: '-ApiKey "$(ApiKey)" -EntityGuid "$(EntityId)" -Version "1.0.0" -Description "Deployed by Azure CI/CD" -User "DevOps"'
    pwsh: true

By default, a build agent does not create ProjectName folder. It just checkouts to the root of $(Build.SourcesDirectory). You may try:

filePath: '$(Build.SourcesDirectory)\ProjectName\Scripts\pwsh\PowerShell1.ps1'

or just a relative path from the current folder:

filePath: './Scripts/pwsh/PowerShell1.ps1'

I am going to make this an answer as the story is a bit long

You do not have a specific checkout task or download artifact task in your YAML, meaning the repository is checked out directly (not with a project/artifact or repository name) into the sources directory. So what do you mean by 'ProjectName'?, is that a folder in the root of the repository? Or is 'scripts' in the root of the repository?

You have to make the path after $(Build.SourcesDirectory) relative from the root in the repository used by the pipeline.

Other artifacts used will be added to the sourcesdirectory with their relative name,

for example:

- download: current
  artifact: some-drop

will be located in $(Build.SourcesDirectory)\some-drop\

But this is not the case for you