Invalid Characters in Add-PnPFile stream output - powershell

Question

I am trying to take a string and write it to a new file (or update an existing file) in SharePoint Online. Using the following code, the file is created, but it is full of invalid characters (? inside a diamond) and the string "test string" does not appear.
$RootPath = '/Shared Documents/General'
$FolderName = 'Customer'
$FileName = 'test.txt'
$fileContent = 'test string'
$Size = 8192;
[System.IO.MemoryMappedFiles.MemoryMappedFile]$MMF = [System.IO.MemoryMappedFiles.MemoryMappedFile]::CreateNew($FileName, $Size);
If ($Null -eq $MMF) {
Return;
}
$Stream = $MMF.CreateViewStream();
$StreamWriter = [System.IO.StreamWriter]::new($Stream);
$StreamWriter.Write($FileContent);
Add-PnPFile -FileName $FileName -Folder "$RootPath/$FolderName" -Stream $Stream
$StreamWriter.Dispose();
$Stream.Dispose();
$MMF.Dispose();
Am I encoding the string incorrectly or what?

Answer 1

Sample script for your reference.
#region Variables
$Username = "user#xxx.onmicrosoft.com"
$Password = "Password"
$siteURL = "https://xxx.sharepoint.com/sites/lee"
#endregion Variables
#region Credentials
[SecureString]$SecurePass = ConvertTo-SecureString $Password -AsPlainText -Force
[System.Management.Automation.PSCredential]$PSCredentials = New-Object System.Management.Automation.PSCredential($Username, $SecurePass)
#endregion Credentials
Connect-PnPOnline -Url $siteURL -Credentials $PSCredentials
$RootPath = '/Shared Documents/General'
$FolderName = 'Customer'
$FileName = 'test.txt'
$fileContent = 'test string'
$Stream = [IO.MemoryStream]::new([Text.Encoding]::UTF8.GetBytes($fileContent))
# $Size = 8192;
# [System.IO.MemoryMappedFiles.MemoryMappedFile]$MMF = [System.IO.MemoryMappedFiles.MemoryMappedFile]::CreateNew($FileName, $Size);
# If ($Null -eq $MMF) {
# Return;
# }
# $Stream = $MMF.CreateViewStream();
# $StreamWriter = [System.IO.StreamWriter]::new($Stream);
# $StreamWriter.Write($FileContent);
Add-PnPFile -FileName $FileName -Folder "$RootPath/$FolderName" -Stream $Stream
# $StreamWriter.Dispose();
# $Stream.Dispose();
# $MMF.Dispose();
Write-Host "----"