HTTP 520 Errors still persisting

I get 521 error.

Kindly, follow the steps in the article and the post from below to solve your issue:

Moreover, do you have an valid SSL certificate at your origin/host for your domain and your sub-domains? Also, which SSL mode have you got enabled (Full SSL, …)?

https://support.cloudflare.com/hc/en-us/articles/115003011431-Troubleshooting-Cloudflare-5XX-errors#521error

https://support.cloudflare.com/hc/en-us/articles/201897700-Allowing-Cloudflare-IP-addresses