Unable to open subdomain one.example.com: This site can’t be reached DNS_PROBE_FINISHED_NXDOMAIN

Applicable to:

Website's subdomain one.example.com cannot be opened with the following error:

CONFIG_TEXT: This site can’t be reached
DNS_PROBE_FINISHED_NXDOMAIN
The main domain example.com is accessible without any issues.
The DNS checker https://mxtoolbox.com/ shows that DNS record is not published:

Missing DNS record (type A) for subdomain one.example.com.

If DNS zone is managed by DNS server in Plesk:
1. Log into Plesk UI.
2. Add record (type A) for the one.example.com subdomain via Plesk > Domains > example.com > DNS Settings > Add Record:
3. Click the OK button.
If DNS zone is managed by DNS provider:

Contact DNS provider to create required A record for domain one.example.com.