How do I file a complaint against a domain owner?

This domain
swaganmiscamitan.gq
and in particular this address

is used by a fraudster.
He forged a page of a large Ukrainian marketplace.

If you feel that a site is engaging in illegal or inappropriate activities, you can submit an abuse report at https://cloudflare.com/abuse. The Trust and Safety team will then review the details and reply if appropriate. You can also report the site to your relevant local authorities.