Thanks for sending the report issue. Can you please go to the root folder where the IWP is installed, please find the config.php file and the following lines.
//multicall options
define('MULTICALL_FILE_BLOCK_SIZE', 5); //MB
define('MULTICALL_LOOP_BREAK_TIME', 11); //SECS
define('MULTICALL_UPLOAD_BLOCK_SIZE', 5); //MB
Please add these lines and then try multicall backups and let me know what happened.