Hi there,
This is a server error (https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/502) usually caused by bad configuration from your Hosting provider. Here https://www.cssigniter.com/kb/errors-when-importing-sample-content/ you can find a list of all possible reason this error might occur, and you will need to address them to your host.
Another option is to manually download sample content from here https://www.cssigniter.com/sample_content/nozama-lite.zip
Extract the zip file you downloaded and upload the xml file in Tools > Import > WordPress (if not already present, you will be prompted to install the WordPress importer plugin), assign the authors to an existing user and make sure you check the “import attachments” box. You can now import the sample content.
You can then import the widgets you see on the theme’s demo. To do that, you need the Widget Importer & Exporter plugin. To install it go to Plugins > Add new search for widget importer exporter and install the plugin. Activate it and go to Tools > Widget Importer & Exporter click choose file and upload the olsen-light-widgets.wie file which is located in the sample content zip file, click Import widgets and you are good to go.
WARNING: As this will create posts, pages, custom post types, categories, widgets, etc. and change various system settings, it is strongly advised that you do this on a clean WordPress installation, without any previous and/or precious data. Under no circumstances we can be held responsible for total or partial data loss, so please be careful.
I suggest to avoid timeouts, to select while importing sample content not to import media (images).
Let me know if you need additional help on this.
