Current Drupal 8 version is 8.5. Please make sure that you are using latest PHP version on your server, for this newest version, Drupal requires at least PHP 7.1. If you can’t use this version on your server then you need to delete vendor folder and run “composer update” command to get an older versions of the plugins.

Demo: https://themeforest.net/item/rhythm-multipurpose-commerce-drupal-theme/10876314