It is not necessary 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.
Note: Before using 1&1 Ionos for a subdomain, enable the service for your main domain.
When your main domain is active in Ionos, add a subdomain.
Ionos configurations:
Sign in to your Ionos account.
In the Dashboard navigate to the Your domain panel and click on Manage Domain:
In the next screen click on DNS:
Click on Add record:
In the next screen click on the CNAME option:
Enter the following values and click on Save:
Host Name: <your-subdomain-name>
Points to: cname.short.io
For example:
Short.io configurations:
Sign in to your Short.io account.
Open the User menu and click on Add domain:
In the next screen click on Add my own domain:
Enter your domain name, select This is domain I already use for website or blog.
Select an option according to your subdomain name and click on Add domain:
Open the Domain settings and check if the domain is in status Active:
Important note: If the domain is Inactive then wait for a few hours and click on Refresh to check if the status has changed.
You will receive an email from the Short.io team informing you that the domain is now configured. Feel free to shorten your links and enjoy Short.io.