Xstore Core plugin requires the following theme: Xstore v5.1 or higher.
Downgrade the plugin to version 1.0.23 to use it with the current theme version. 1.0.23 plugin version you can find this here
However I had issues a few weeks back where I had updated the theme and the Xstore core plugin was not compatible with the version of the theme I used – so someone on here downgraded my theme to version 5.0.3 – the site worked fine for a while but now this has happened
I am glad that your problem was solved.
If you need our help, do not forget to provide dashboard access also.
About Core plugin updating, you can simply delete the plugin via dashboard then go to XStore > Install plugins > install the latest version of Core plugin.
To update premium plugins, connect to your server using FTP. Copy extracted plugins folders into wp-content/plugins/ . The latest versions of plugins you can find here – https://www.8theme.com/download-plugins/