Depending on the version of the module, the security hash may be missing and when this happens indexing fails. You'll get the following error:
Your server is forbidding access to your feed. Please check file access and feed url – [products][URL]
To fix this, go to the Support tab in the plugin configuration in your Prestashop account and click on the 'Enable advanced module tab options' link.
An Advanced tab will be displayed with the feed URL information:
Copy and paste the feed URL in your Admin Panel > Search Engines > Settings > Indices and reindex the feed by selecting the Process Now button.