Hi,
Thank you for reaching out us. I’m sorry that you’re experiencing issues.
Upon further checking halisbayancuk.com, I can see that 521 errors are no longer happening since 27th of October. Can you please confirm if you’re still facing issues? If so, please refer to our docs here: Troubleshooting Cloudflare 5XX errors | Cloudflare Support docs
I hope this helps. Please let us know if you still have questions.
Kindly,