404 issue

@dufbenpp the example you provided does not seem to have any relevance to Asset CleanUp Pro. It’s not a file generated by the plugin as all the files that are optimized are stored in /wp-content/cache/asset-cleanup/.

Based on the research I did, it’s likelt connected to an SSL certificate. Here’s an article that explains it where both “.well-known” and “pki-validation” directories are mentioned: https://qodeinteractive.com/magazine/how-to-add-free-ssl-certificate-wordpress/