We do not block or challenge any requests from Facebook by default. However, some of our users see attempts to post their site to Facebook return an Attention Required error. This appears when : 

• the security level is set to “I’m Under Attack” (either globally or via a Page rule).
• there is a user-defined firewall challenge/block that includes a Facebook IP (note that these IPs can be covered by a country challenge too–Facebook is known to crawl from both the US and Ireland)

To resolve these issues, you can either remove the corresponding firewall rule(s), or explicitly whitelisting AS32934 and AS63293 in your IP Firewall, which will override the challenge/block rules and the Under Attack challenge.

If you previously had issues with Facebook, you may find it necessary to re-scrape pages. You can do so using the Fetch New Scrape Information option on Facebook’s Object Debugger, as Facebook only re-scrapes content every 30 days unless instructed otherwise. If you need to update a large number of resources, Facebook provides an API that can help you do so.

If you still have issues, please contact support mentioning :
–  the URLs of your website you can’t share on Facebook
–  the output from Facebook’s debug tool
–  Confirm you have re-scraped the URLs