This error is usually caused by security settings on the site, or the sever side, which are blocking the file uploading.

To solve the issue, please check and change the relevant security settings on the site or the server to allow the uploading.

Alternatively, you can use FTP or file manager to upload the backup to the /wpvividbackups directory in the /wp-content directory of the site, then click ‘Scan uploaded or received backups’ on WPvivid to display it in the backup list.