Security scoped Bookmarks iOS - Swift

Hey, I am trying to save the url which I get from my didPickDocumentAt as a security scoped bookmark

This is my code:

Here just the declaration of the UIDocumentPickerViewController

let documentPicker = UIDocumentPickerViewController(documentTypes: [kUTTypePlainText as String], in: .open)

documentPicker.delegate = self
if #available(iOS 11.0, *)
{
     documentPicker.allowsMultipleSelection = false
}
else
{
    // Fallback on earlier versions
}
present(documentPicker, animated: true, completion: nil)

Now didPickDocumentAt - there I am saving my bookmark data from my selected file on the smb server. Data.bookmarkAdmin is just the variable in which I store the bookmark.

func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentAt url: URL)
{
    print(url)
        
    do
    {
        let shouldStoppAccessing = url.startAccessingSecurityScopedResource()
        defer
        {
            if shouldStoppAccessing
            {
                url.stopAccessingSecurityScopedResource()
            }
        }

        let bookmarkData: Foundation.Data = try url.bookmarkData()
            
        Data.bookmarkAdmin = bookmarkData
        print(Data.bookmarkAdmin)
    }
    catch let error
    {
        print(error)
    }
}

Later in my app I want to use the bookmark data to create the url again and write on that file

func readFile()
{
    Admin.fileContent = ""
    Admin.readString.removeAll()
        
    do
    {
        var isStale = false
        
        let url = try URL(resolvingBookmarkData: Data.bookmarkAdmin, bookmarkDataIsStale: &isStale)

        guard !isStale
        else
        {
            return
        }
        
        var errorText: Error?
                do
                {
                    let didStartAccessing = url.startAccessingSecurityScopedResource()
                    defer
                    {
                        if didStartAccessing
                        {
                            url.stopAccessingSecurityScopedResource()
                        }
                    }

                    print(url)
                    let fileURLs =  try FileManager.default.contentsOfDirectory(at: url, includingPropertiesForKeys: nil)
                        Admin.fileContent = try String(contentsOf: fileURLs[0], encoding: .utf8)
                        print("ADMIN: \(Admin.fileContent)")
                    }
                    catch
                    {
                        errorText = error
                    }
                    
            //        Errorhandling
                    if errorText != nil
                    {
                        let alertController = UIAlertController(title: "Error", message: "Keine Datei gefunden \(String(describing: errorText))", preferredStyle: .alert)
                        
                        let okAction = UIAlertAction(title: "ok", style: .default, handler: nil)
                        
                        alertController.addAction(okAction)
                        
                        present(alertController, animated: true, completion: nil)
                    }
                    else {}
        }
    catch let error {}
}

I get an error in my readFile() function ERROR:

Error Domain=NSCocoaErrorDomain Code=256 "The file “testaufbau” couldn’t be opened." UserInfo={NSURL=file:///private/var/mobile/Library/LiveFiles/com.apple.filesystems.smbclientd/ctPrTwTestApp/testaufbau.csv, NSFilePath=/private/var/mobile/Library/LiveFiles/com.apple.filesystems.smbclientd/ctPrTwTestApp/testaufbau.csv, NSUnderlyingError=0x2834bfbd0 {Error Domain=NSPOSIXErrorDomain Code=20 "Not a directory"}}

When I set the url manually in the readFile() without the bookmark just

let url: URL = URL(fileURLWithPath: "/private/var/mobile/Library/LiveFiles/com.apple.filesystems.smbclientd/ctPrTwTestApp/testaufbau.csv")

Then I get a different ERROR:

Error Domain=NSCocoaErrorDomain Code=257 "The file “testaufbau.csv” couldn’t be opened because you don’t have permission to view it." UserInfo={NSURL=file:///private/var/mobile/Library/LiveFiles/com.apple.filesystems.smbclientd/ctPrTwTestApp/testaufbau.csv, NSFilePath=/private/var/mobile/Library/LiveFiles/com.apple.filesystems.smbclientd/ctPrTwTestApp/testaufbau.csv, NSUnderlyingError=0x280ac1440 {Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"}}

How can I solve this and how do I get permission?