Challenge update failures for khongcotien.top in order https://acme-staging-v02.api.letsencrypt.org/acme/order/5751349/1579400348
acme: error code 400 "urn:ietf:params:acme:error:dns": DNS problem: NXDOMAIN looking up TXT for _acme-challenge.khongcotien.top - check that a DNS record exists for this domain