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 Squarespace for a subdomain, enable the service for your main domain.
When your main domain is active in Squarespace, add a subdomain.
Squarespace configurations:
Sign in to your Squarespace account.
In the top left corner of the page click on Domains:
Click on the domain that you want to connect with Short.io:
In the Overview panel click on DNS:
Click on Add record.
In the Custom records panel fill in the following information and click on Save.
Host: <your-subdomain-name>
Type: CNAME
Data: cname.short.io
The result should look similar to:
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.