If you have one domain and then one (or more domains) that redirects to that domain, then you only need a subscription for the one domain.
It is important to note that if a website user can access content on a website, then that domain needs a subscription. If it redirects so that the user can never actually access content on that website, then you don’t need a subscription for it. In that case, just add the one domain that is being redirected to in the backend Manager on your Cookiebot account.
If you have multiple identical websites – for example because you display the same content on various domains (without redirecting), then please see I have multiple websites with identical content. Do I need a subscription for each domain?