Solution: 520: Web server is returning an unknown error

The message „520: Web server is returning an unknown error” can be caused by various reasons. If you are facing this error in your open graph title field, please note that this behavior on your website is caused by a “Cloudflare” configuration on your website. The following instructions will show you how to proceed.

First of all, it is important to make sure that the information and metadata of the source code on your website (image, link description, etc.) can be retrieved correctly by the social networks to avoid issues when posting on social media.

Here are some solutions provided by the Cloudflare support:

Troubleshooting Error 520 (Cloudflare community forum):
https://community.cloudflare.com/t/community-tip-fixing-error-520-web-server-is-returning-an-unknown-error/44205
https://support.cloudflare.com/hc/en-us/articles/115003011431-Troubleshooting-Cloudflare-5XX-errors#520error

If this error still appears for you afterwards, please contact the Cloudflare support team since this issue is outside of our sphere of influence:
https://support.cloudflare.com/hc/en-us/articles/200172476
https://support.cloudflare.com/hc/en-us

You also can check the way your posts will be displayed on social media with the following tools:
Facebook Sharing Debugger
Twitter Card Validator
LinkedIn Post Inspector

In addition, these guides show you:
What are open graph tags and what do I use them for?
Link Preview - Troubleshooting checklist and solutions for setting Open Graph Tags