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Someone in Facebook posted a link to my site. Facebook tries to show a preview of the page with the link but it only shows "403 Forbidden". I am sure that I am somewhere blocking this Facebook request but am not sure what the issue is. For example, I only accept GET POST and HEAD requests and perhaps this is some other kind of request.

The link looks like this (with the site name changed).

<a class="_52c6" href="https://www.example.com/index.php?topid=1&amp;grade=4&amp;page=Movement" tabindex="-1" target="_blank" data-lynx-mode="async" rel="nofollow" data-lynx-uri="https://l.facebook.com/l.php?u=https%3A%2F%2Fwww.example.com%2Findex.php%3Ftopid%3D1%26grade%3D4%26page%3DMovement&amp;h=ATMXgEds4Ymh3lFXLPXBbWVCIpDtJE_0gYVzgWTVdbsPfrBr6vIr7CJhYxkxDpQpB-js2Yl91RpOiRU5q8XFbZyvtVspSVZ6WG7tIB6rQkV2-nP8iIskWlN5Tha441w7nfGx9aaby2TmQdT9QMNt0IpGsXttslzB6GXaX7fnbgWJyHfCyJN-BdTKtO9V-gXtJc6IFiRqcSsa57JSXgNDTRq50D-dkMIl4YLFaUYN4xL8ozIOZMakcDxjgksMUx9G"></a>

Each time I load the Facebook page, I would expect to get a request in my server log that I am blocking, but I don't see any. Can you help me pinpoint what is going on here?

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  • Facebook doesn't refresh the preview on every page load. Try sharing a new link to your site and look for requests from the user agent facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php) Oct 23 '17 at 16:42
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    That was it. I have a long list of "bad bots" that I block access to in order to reduce traffic and this user agent was added to it. My list is kept and processed in php but if a certain threshold of hits is reached from a "bad bot" user agent, then that user agent is automatically added to a RewriteCond in .htaccess. Because it was added to .htaccess, my error log of blocked requests (generated in php) didn't contain a trace of it. It is good to know my .htaccess blocking is working.
    – mseifert
    Oct 24 '17 at 4:08
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The Facebook Sharing Debugger is the tool you want - you need to be logged in to Facebook to use it.

This will allow you to test a URL, and see both what Facebook has cached, and request an updated scrape:

Example response for a URL

You can also submit a list of URLs that you'd like to be invalidated from the Cache so that you can refresh a bunch of pages if required.

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