I am trying to upload media files to WordPress from an external API provider.
I have written a few codes, but it’s not importing anything.
I have no idea what is going wrong.

My codes are:

function import_external_media() {
    // Set API endpoint URL, using local instance for now
    $api_url="http://localhost/media";

    // Fetch media data from API
    $response = wp_remote_get( $api_url );
    if ( is_wp_error( $response ) ) {
        // Handle error
        return;
    }

    $media_data = json_decode( wp_remote_retrieve_body( $response ), true );

    // Set target directory for media files
    $upload_dir = wp_upload_dir();
    $target_dir = $upload_dir['basedir'] . '/external-media/';

    // Create target directory if it doesn't exist
    if ( ! file_exists( $target_dir ) ) {
        mkdir( $target_dir, 0755, true );
    }

    // Import media files
    foreach ( $media_data as $media ) {
        $media_url = $media['url'];
        $media_name = basename( $media_url );
        $target_path = $target_dir . $media_name;

        // Check if file already exists
        if ( file_exists( $target_path ) ) {
            continue;
        }

        // Fetch media file from URL
        $file_data = wp_remote_get( $media_url );
        if ( is_wp_error( $file_data ) ) {
            // Handle error
            continue;
        }

        // Save media file to target directory
        $saved = file_put_contents( $target_path, wp_remote_retrieve_body( $file_data ) );
        if ( $saved === false ) {
            // Handle error
            continue;
        }

        // Add media file to media library
        $attachment = array(
            'guid' => $upload_dir['baseurl'] . '/external-media/' . $media_name,
            'post_mime_type' => $media['mime_type'],
            'post_title' => $media['title'],
            'post_content' => '',
            'post_status' => 'inherit'
        );
        $attachment_id = wp_insert_attachment( $attachment, $target_path );

        // Generate metadata for attachment
        require_once( ABSPATH . 'wp-admin/includes/image.php' );
        $attachment_data = wp_generate_attachment_metadata( $attachment_id, $target_path );
        wp_update_attachment_metadata( $attachment_id, $attachment_data );
    }
}

// Hook into WordPress cron system to run import on schedule
add_action( 'wp_scheduled_event', 'import_external_media' );

My json structure is:

"fields": {
    "title": "Playsam Streamliner",
    "file": {
      "fileName": "ladybug-7877480_960_720.jpg",
      "contentType": "image/jpg",
      "details": {
        "image": {
          "width": 600,
          "height": 446
        },
        "size": 27187
      },
      "url": "https://cdn.pixabay.com/photo/2023/03/26/03/12/ladybug-7877480_960_720.jpg"
    }
  }