Facebook link preview not showing for a phpBB3 forum post

Question

I have this forum running on phpBB3 forum software. It is working fine by itself. But when I try to add a forum post link on facebook, it does not show preview of the page. When I tried this with facebook debugger (https://developers.facebook.com/tools/debug/), it shows me RNF error (HTTP 404) for my post because it does not append required parameters to the URL.

This is what I see on the facebook debugger page -

Scrape Information
Response Code   404
Fetched URL http://mysite.tld/forums/viewtopic.php?f=9&t=25
Canonical URL   http://mysite.tld/forums/viewtopic.php?f=9&t=25
Final URL   http://mysite.tld/forums/viewtopic.php

Is there a way to tell facebook to consider the query parameters of the URL as well? I did try adding og:XXX tags in the header but it didn't help in any way and I continue to see 404 errors in facebook debugger.

I do not think adding tags is a problem because I tried this URL in facebook debugger and it could feth the title and all other details correctly for this URL.

https://www.phpbb.com/community/viewtopic.php?f=72&t=2120397

And I see that these forums do not have any face og:XXX tags here.

What might be causing problem for my forums and how can I fix it?

Any pointers, inputs would be highly appreciated!

TIA, - Manish

I have already searched the questions here, and didn't find any pointer. I have already done my homework regarding facebook debugger and link preview, so not sure why it has been voted down.

Answer 1

I have figured it out. As it turned out - the bots didn't have the cookie set and hence were getting HTTP 404 response (a possible bug in custom style: fresco). Once I realized that this problem was due to cookies, I edited all the bots (ACP >> General >> Spiders/Robots) to use default phpBB style prosilver. Once that was fixed, facebook started showing link previews properly!