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 Store tab in the plugin configuration in your Prestashop account and check the Store section.
Take a look at Feed URLs to use on Doofinder Admin Panel
Copy and paste the feed URL in your Admin Panel > Search Engines > Settings > Indices and reindex the feed by selecting the 'Process Now' button.
