Suddenly the domain stopped working, other domains are working fine

[deltanw]

The server behind the domain is working fine and the cloudflare proxy is off

[simon]

You need to contact your domain Registrar, hostinger as your domain appears to be in a serverHold status:

How to Check a Domain Status on WHOIS | Hostinger Help Center

From WHOIS for your domain:

# whois.nic.site

Domain Name: DELTASUB.SITE
Registry Domain ID: D375833880-CNIC
Registrar WHOIS Server: whois.hostinger.com
Registrar URL: https://www.hostinger.com/
Updated Date: 2023-08-14T10:12:43.0Z
Creation Date: 2023-06-21T06:29:22.0Z
Registry Expiry Date: 2024-06-21T23:59:59.0Z
Registrar: HOSTINGER operations, UAB
Registrar IANA ID: 1636
Domain Status: serverHold https://icann.org/epp#serverHold
Domain Status: serverTransferProhibited https://icann.org/epp#serverTransferProhibited
Domain Status: clientTransferProhibited https://icann.org/epp#clientTransferProhibited
Registrant Organization: Privacy Protect, LLC (PrivacyProtect.org)
Registrant State/Province: MA
Registrant Country: US
Registrant Email: Please query the RDDS service of the Registrar of Record identified in this output for information on how to contact the Registrant, Admin, or Tech contact of the queried domain name.
Admin Email: Please query the RDDS service of the Registrar of Record identified in this output for information on how to contact the Registrant, Admin, or Tech contact of the queried domain name.
Tech Email: Please query the RDDS service of the Registrar of Record identified in this output for information on how to contact the Registrant, Admin, or Tech contact of the queried domain name.
Name Server: POPPY.NS.CLOUDFLARE.COM
Name Server: LANGSTON.NS.CLOUDFLARE.COM
DNSSEC: unsigned
Billing Email: Please query the RDDS service of the Registrar of Record identified in this output for information on how to contact the Registrant, Admin, or Tech contact of the queried domain name.
Registrar Abuse Contact Email: [email protected]
Registrar Abuse Contact Phone: +370.68424669
URL of the ICANN Whois Inaccuracy Complaint Form: https://www.icann.org/wicf/
>>> Last update of WHOIS database: 2023-08-14T13:12:11.0Z <<<

Notice Domain Status: serverHold https://icann.org/epp#serverHold there.

Your nameservers are set according to WHOIS, but they are not being returned by the .site root nameservers, presumably due to the serverHold status:

dig @a.nic.site. deltasub.site NS

; <<>> DiG 9.18.17 <<>> @a.nic.site. deltasub.site NS
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 729
;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;deltasub.site.			IN	NS

;; AUTHORITY SECTION:
site.			3600	IN	SOA	ns0.centralnic.net. hostmaster.centralnic.net. 356578 900 1800 6048000 3600

;; Query time: 54 msec
;; SERVER: 194.169.218.61#53(a.nic.site.) (UDP)
;; WHEN: Mon Aug 14 14:14:31 WEST 2023
;; MSG SIZE  rcvd: 107

Notice NXDOMAIN in the response there from the .site root servers.

Contact Hostinger and they will be able to advise on how you can fix this.