Backup and Restore a Flutter SQLite database file to iCloud

I'm managing the database with SQLite in Flutter. I want to enable iCloud backup and restore on the Swift side when called from Flutter. I am using the following source code, but it is not working. What could be the cause? Could you provide a method and countermeasure?

    private func saveFileToICloud(fileName: String, localDatabasePath: String, result: @escaping FlutterResult) {
        guard let containerName = Bundle.main.object(forInfoDictionaryKey: "ICLOUD_CONTAINER_NAME") as? String else {
            result(FlutterError(code: "NO_ICLOUD_CONTAINER", message: "iCloud container is not available", details: nil))
            return
        }
        guard let containerURL = FileManager.default.url(forUbiquityContainerIdentifier: containerName) else {
            result(FlutterError(code: "NO_ICLOUD_CONTAINER", message: "iCloud container is not available", details: nil))
            return
        }
        let fileURL = containerURL.appendingPathComponent(fileName)
        let sourceURL = URL(fileURLWithPath: localDatabasePath)
        do {
            if FileManager.default.fileExists(atPath: fileURL.path) {
              try FileManager.default.removeItem(at: fileURL)
            }
            try FileManager.default.copyItem(at: sourceURL, to: fileURL)
            result("File saved successfully to iCloud: \(fileURL.path)")
        } catch {
            result(FlutterError(code: "WRITE_ERROR", message: "Failed to write file to iCloud", details: error.localizedDescription))
        }
    }

    private func readFileFromICloud(fileName: String, localDatabasePath: String, result: @escaping FlutterResult) {
        let containerName = ProcessInfo.processInfo.environment["ICLOUD_CONTAINER_NAME"]
        guard let containerURL = FileManager.default.url(forUbiquityContainerIdentifier: containerName) else {
            result(FlutterError(code: "NO_ICLOUD_CONTAINER", message: "iCloud container is not available", details: nil))
            return
        }
        let fileURL = containerURL.appendingPathComponent(fileName)
        let sourceURL = URL(fileURLWithPath: localDatabasePath)
        do {
            if FileManager.default.fileExists(atPath: sourceURL.path) {
                try FileManager.default.removeItem(at: sourceURL)
            }
            try FileManager.default.copyItem(at: fileURL, to: sourceURL)
            result("File restored successfully to sqlite: \(sourceURL.path)")        } catch {
            result(FlutterError(code: "READ_ERROR", message: "Failed to read file from iCloud", details: error.localizedDescription))
        }
    }