Saving Hosting Settings on Plesk for Linux fails: JSON.parse: Unexpected non-whitespace character after JSON at position 19198 of the JSON data, zone example.com/IN: has no NS records

Symptoms

• In Plesk on a Linux server, saving domain's Hosting Settings in the menu Domains > example.com > Hosting & DNS > Hosting fails:

  JSON.parse: Unexpected non-whitespace character after JSON at position 19198 of the JSON data, zone example.com/IN: has no NS records

• The following errors are written to the Plesk log file /var/log/plesk/panel.log and to the system log file /var/log/messages (or /var/log/syslog):

  Note: the error may be about the parent domain of the affected domain.

  ==> /var/log/messages <==
  plesk.example.com dnsmng[13817]: Dns zone candidate file '/var/named/chroot/var/example.com.next' is not valid (strictMode:1). Changes are reverted. Reason:
  plesk.example.com dnsmng[13817]: > zone example.com/IN: has no NS records
  plesk.example.com dnsmng[13817]: > zone example.com/IN: not loaded due to errors.
  plesk.example.com dnsmng[13817]: Candidate dns zone file for 'example.com' is invalid. Likely there is some inconsistency in the database
  
  ==> /var/log/plesk/panel.log <==
  13384:66796ea20de86 ERR [util_exec] proc_close() failed ['/usr/local/psa/admin/bin/dnsmng' '--update' 'example.com' '--without-reverse'] with exit code [1]
  13384:66796ea20de86 ERR [panel] '/usr/local/psa/admin/bin/dnsmng' '--update' 'example.com' '--without-reverse' failed with code 1.
  
  stdout:
  
  stderr:
  
  13384:66796ea20de86 ERR [panel] Error during example.com updateZone: dnsmng failed: :
  0: /usr/local/psa/admin/plib/Service/Dns/Connector/Plesk.php:14
  Service_Dns_Connector_Plesk->commitChanges()
  1: /usr/local/psa/admin/plib/Service/Dns/Connector/Proxy.php:207
  Service_Dns_Connector_Proxy->commitChanges()
  2: :

  The same error as in the Plesk log file /var/log/plesk/panel.log is visible in the browser console/DevTools: "Network" tab > graphql request > "Response".

• After creating a subdomain in already existing subscription in Plesk, different system/configuration files are not created in the directory /var/www/vhosts/system/one.example.com/, for example, the file php-fpm.sock or web server configuration files under /var/www/vhosts/system/one.example.com/conf.
  An error similar to ones shown above is written to the log file /var/log/plesk/panel.log.

Cause

There are no NS records in the DNS zone of the domain highlighted in the error Domains > example.com > Hosting & DNS > DNS.

Resolution

Add at least one NS record (and the A record for the NS record value hostname) in Domains > example.com > Hosting & DNS > DNS.