The custom domain URL is the custom vanity domain you want to point to your Geo Link in your account.
You can either use a new domain or an existing domain which is currently hosting your website. See a quick guide here on how to do this: https://help.geotargetly.com/en/articles/3806612-geo-link-custom-domains-quick-start-guide
Using a new domain
Register a new domain using your preferred domain registrar. Once you setup the custom domain in Geo Targetly, you will be provided with DNS instructions which you will need to modify
Using an existing domain already connected to a website
You can also use an existing domain that is currently connected to your website. A separate page (e.g. yourdomain.com/link) can be reserved to map to all your Geo Links.
Setup the custom domain in Geo Targetly as yourdomain.com/{page-name}. Ensure that this page name is not used by any other page on your site. Once you setup the custom domain in Geo Targetly, you will be provided with DNS instructions which you will need to modify for the domain.