Please substitute these with appropriate values for host, domain, password and IP:
https://dynamicdns.park-your-domain.com/update?host=[host]&domain=[domain_name]&password=[ddns_password]&ip=[your_ip]
Fields that are to be changed in the URL are: [host], [domain_name], [ddns_password] and [your_ip].
Here is an example for IP address update for a bare domain (e.g., yourdomain.tld):
Host = @
Domain Name = yourdomain.tld
Dynamic DNS Password = Domain List >> click Manage next to the domain >>Advanced DNS tab >> Dynamic DNS. If it is not enabled, enable it to check the password.
IP Address = optional value. If you don't specify any IP, the IP from which you are accessing this URL will be set for the domain.
NOTE: The values for the host name and domain in the URL must be of the same case (lowercase/uppercase) as in your account.
If the domain is shown as YourDomain.tld in your Dashboard, enter it in the same way: https://dynamicdns.park-your-domain.com/update?host=@&domain=YourDomain.tld&password=e747d77054a844409c486973cb&ip=127.0.0.1
If it shown in lowercase, like yourdomain.tld, add just yourdomain.tld. The URL will have the following format in this case: https://dynamicdns.park-your-domain.com/update?host=@&domain=yourdomain.tld&password=e747d77054a844409c486973cb&ip=127.0.0.1
Please make sure you are using your Dynamic DNS password and not the Namecheap account's one.
To dynamically update the IP address for a subdomain (test.yourdomain.tld), use test for Host (host=test). To dynamically update it for www.yourdomain.tld, use www for Host: host=www.
To have the wildcard subdomain updated dynamically, just make sure that you insert an asterisk (*) as Host in the URL.
TIP: If you don't want to use any DNS client, you can just bookmark the URL (after inputting proper values there) and access it whenever you need to update your IP.