Caution: Connecting directly your existing domain (on which you already host your website) with Short.io can lead to unexpected and unwanted redirects due to the specific DNS settings.
There are two solutions to the above issue:
You can add a subdomain to your domain and shorten links with it.
For more details, please follow the link: https://help.short.io/en/articles/4065825-general-subdomain-setup-instruction
Or
You can purchase a domain for link shortening from Short.io.
The advantage of buying a domain from Short.io is that the domain will be active at once.
For more details, please follow the link: https://help.short.io/en/articles/4065810-how-to-buy-a-domain-on-short-io