Power Shell Error: Exception calling "ExecuteQuery" with "0" argument(s): "File Not Found."

Question

I am building a script to essentially copy an entire directory to a SharePoint online library. I have gotten as far as building the folder directory on SharePoint but cannot seem to load any files onto the online directory. I believe I am really close to cracking this beast, I just need to solve one last error. The full error and my code are listed below:

I have bolded line #109

Exception calling "ExecuteQuery" with "0" argument(s): "File Not Found." At line:109 char:5 + $clientContext.ExecuteQuery() + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + CategoryInfo : NotSpecified: (:) [], MethodInvocationException + FullyQualifiedErrorId : ServerException

...

 ###################### copy files 
cls
$t1  = get-date
$i=1
$count = ((Get-ChildItem -File  -Recurse -Path $source_folder) | Measure-Object -Property FullName ).Count
foreach ($file in (Get-ChildItem -File  -Recurse -Path $source_folder))
{
    $t01  = get-date
    #$url_dest = $url_sharepoint+$Url_site+$file.FullName.Substring($file.FullName.IndexOf($MainFolder)-1).ToLower().Replace('\','/')
    #$url_dest = $url_sharepoint+$Url_site+'/'+$library+(($file.FullName.ToLower()).Replace($source_folder.ToLower(),'')).Replace('\','/')
    $url_dest = $url_sharepoint+$Url_site+$library+$file.FullName.Substring($file.FullName.IndexOf($MainFolder)-1).ToLower().Replace('\','/')
    $FileStream = New-Object IO.FileStream($File.FullName,[System.IO.FileMode]::Open)
    $FileCreationInfo = New-Object Microsoft.SharePoint.Client.FileCreationInformation
    $FileCreationInfo.Overwrite = $true
    $FileCreationInfo.ContentStream = $FileStream
    $FileCreationInfo.URL = $url_dest
    $Upload = $mylist.RootFolder.Files.Add($FileCreationInfo)
    $listItem = $upload.ListItemAllFields
    $listItem['Title']=($file.Name).split('.')[0]
    Write-Host " Uploading file $i/$count $url_dest"
    $listItem.update()
    $clientContext.Load($Upload)
    **$clientContext.ExecuteQuery()**
    $t02  = get-date
    $speed ="{0:n2}" -f ($file.Length/($t02-$t01).TotalSeconds/1mb)
    Write-Host "...................upload speed was " $speed " MB/sec"
    $i++

    $FileStream.Close()
}
$mylist.Title

$t2=get-date
$size = "{0:n2}" -f (gci -path $source_folder -recurse | measure-object -property length -sum).sum

Answer 1

After some debugging... I finally discovered that the file path that the files where trying to upload to was wrong. My path was sharepoint.com/documents/mainfolder/subfolder, but it needed to be sharepoint.com/Shared%20Documents/mainfolder/subfolder.