WP STAGING kept the unfinished-clone guard active because it cannot verify that the staging site's wp-config.php sets $table_prefix to the staging prefix %1$s. Clone and reset copy the live site's wp-config.php, so edit that file: replace its $table_prefix assignment with %2$s and keep it the only one, on a line of its own below every include and directly above the wp-settings.php require. Then reset this staging site, or delete it and clone again.