DNS records must be configured correctly on your ISP in order to point your subdomains to Odoo services. One of the most common mistakes is not to put a period at the end of the domain name.
For example, let's say you need to redirect your "erp.yourdomain.com" address to "servicename.eska.biz".
In this case, in your DNS settings, you should make the CNAME registration for your "ERP" subdomain to be directed to "servicename.eska.biz" as follows;
erp servicename.eska.biz.
If you have noticed, there is a period (.) after "servicename.eska.biz".
If you don't put that dot (.) in your registration, DNS servers will probably not be able to resolve URL and the redirection will not be completed properly.
The second mistake is to write the definitions and values in the wrong places;
servicename.eska.biz erp.yourdomain.com
or
servicename.eska.biz erp
Such misspellings should be avoided.
If you want to see that the redirection is working properly after the registration made, you need to try the "subdomain.yourdomain.com" URL address in the Incognito Window, in our example, "erp.yourdomain.com".
Incognito Window can be opened by pressing the letters CTRL+Shift+N.
Otherwise, your web browser's cache will mislead your request and your web browser will not direct you to the right URL.
The visitor, who will enter the site for the first time, will be redirected to the right URL instantly if you have made the above definition correctly. Some DNS servers may need time between 2 hours and 6 hours for resolving names!