If the spinner is present it means that the initial full sync is in progress. This can take some time depending on the number of products and size of images in your product catalog. You are better leaving this running and doing something else rather than watching it. (Once the first full sync has completed incremental changes are synchronized very quickly).
If the grid is blank without a spinner present it generally means that Codisto LINQ is being denied connection access to perform the sync. This is usually due to server/firewall configurations.
Please ensure IP address: 188.8.131.52 is whitelisted to allow the plugin to sync.
If there are still issues, please send a ticket to firstname.lastname@example.org. If you supply your ecommerce platform admin credentials (and FTP/SSH/C-panel if available) in the initial ticket it will be the efficient way of getting you up and running because we generally require this to diagnose the problem. (The alternative is to get your developers to have a look at the issue but we have seen most issues before and are generally faster to provide feedback on what, if anything, needs to rectified for successful sync).