Add refiners to Refinement webpart

UpdateRefiner.ps1

function GetWebPartByTitle()
{
   param(
      [Parameter(Mandatory=$true, Position=0, ValueFromPipeline=$true)]
      [Microsoft.SharePoint.Client.WebParts.WebPartDefinitionCollection] $webParts,
      [Parameter(Mandatory=$true, Position=1, ValueFromPipeline=$true)]
      [string] $webPartTitle
    )   
   if($webparts.Count -gt 0){  
    Write-Host "Looping through all webparts"  
    foreach($wp in $webparts){ 
      $ctx.Load($wp.WebPart.Properties)  
      $ctx.ExecuteQuery()  
      $propValues = $wp.WebPart.Properties.FieldValues;   
      if($propValues["Title"] -eq $webPartTitle)
       {
         return $wp;  
       }                
    }
  } 
   return $null;  
}

#return webpart based on title passed
function updateSearchRefinerWebPart
{
 param(
        [Parameter(Mandatory=$true, Position=0, ValueFromPipeline=$true)]
          [Microsoft.SharePoint.Client.ClientContext]$ctx,
        [Parameter(Mandatory=$true, Position=1, ValueFromPipeline=$true)]
          [string]$pageUrl
  )
 
   $web = $ctx.Web;
   $page =  $web.GetFileByServerRelativeUrl($pageUrl);
   $ctx.Load($web);
   $ctx.Load($page);
   $ctx.ExecuteQuery();
 
   #Check if page already checked out. If so, undo check out  
if($page.CheckOutType -eq [Microsoft.SharePoint.Client.CheckOutType]::Online){  
    try{  
        Write-Host "Undo Checkout"  
        $page.UndoCheckOut()  
        $ctx.load($page)  
        $ctx.ExecuteQuery()              
    }  
    catch{  
        write-host "Error in checkout.. $($_.Exception.Message)" -foregroundcolor red  
    }  
}  
 
#If page is not checked out, then check out  
if($page.CheckOutType -eq [Microsoft.SharePoint.Client.CheckOutType]::None){  
    Write-Host "Checkout"  
    $page.CheckOut()  
    $ctx.Load($page)  
    $ctx.ExecuteQuery()  
}    

   # Find the Refinement web part
   $lwpm =$page.GetLimitedWebPartManager([Microsoft.SharePoint.Client.WebParts.PersonalizationScope]::Shared);
   $webParts = $lwpm.WebParts;
   $ctx.Load($webParts);
   $ctx.ExecuteQuery();
   $rwp = GetWebPartByTitle -webParts $webParts -webPartTitle 'Refinement'

   $jsonString = @"
    {
    "sortBy" : 0,
    "sortOrder" : 0,
    "maxNumberRefinementOptions" : 15,
    "propertyName" : "",
    "type" : "Text",
    "displayTemplate" : "~sitecollection/_catalogs/masterpage/Display Templates/Filters/Filter_Default.js",
    "displayName" : "",
    "useDefaultDateIntervals" : false,
    "aliases" : [],
    "refinerSpecStringOverride" : "",
    "intervals" : null
 }
"@

   # Refiners are updated by changing the JSON
   #$propValues = $_.WebPart.Properties.FieldValues; 
   $refctljson = $rwp.WebPart.Properties["SelectedRefinementControlsJson"] | ConvertFrom-Json

   $newRefinerJson = ConvertFrom-Json $jsonString
   $newRefinerJson.propertyName = "RefinableString00"
   $newRefinerJson.displayName = "Directorate"
   $refctljson.refinerConfigurations += $newRefinerJson

   $refJson =  ConvertTo-Json $refctljson -Depth 3 -Compress

   $rwp.WebPart.Properties["SelectedRefinementControlsJson"] = $refJson
    Write-Host "Checkin Page after adding refiner to refinement webpart" 
    # Save the changes
   $rwp.SaveWebPartChanges();
   $page.CheckIn('Changed refiner', [Microsoft.SharePoint.Client.CheckinType]::MajorCheckIn)
   $page.Publish('Changed refiner'); 
   $ctx.load($page);
   $ctx.ExecuteQuery();
}