You do not need to register a new domain name for shortening links if you own one that works properly. Create a subdomain, using a domain you already have.
In case you have a website, add a subdomain to your domain and shorten links with it. The advantages are cost saving and brand recognition.
If you didn't find a needed subdomain setup guide in Short.cm support, follow the typical instruction below to configure a subdomain for shortening links.
1. Go to your domain registrar.
2. Choose a needed domain.
3. Open DNS settings.
4. Add one record with following values:
CNAME-record, "yoursubdomain" host, cname.short.io target.
6. Go to Short.io account. Click on "Add new domain".
7. Add a new subdomain+domain name. For example, "link.brand.org."
8. Click on "Add a domain."
9. Domain activation takes a few hours. When a domain is active, you will be notified by the email.