The click tracking domain setting allows users to control what domain shows up when someone visits a page containing a HubSpot CTA. This is an optional setting that helps promote your company's brand to your website visitors.
To configure your CTA click tracking domain settings, navigate to Content > Calls-to-Action > Settings > and select your desired COS hosted domain under Click Tracking Domain; it will save automatically and the updates will be seen when hovering over any existing CTAs placed on your pages.
Please note that any CTA will stop working if you remove the chosen domain from within your Domain Manager in HubSpot. Also, any Email click tracking domain will override a selected CTA click tracking domain.