Hi @alindelbert
Welcome to the Auth0 Community!
Unfortunately, regardless of plan, you are allowed only a single custom domain per tenant. Such an implementation would require a multi-tenant approach. As I have mentioned previously in this community post:
Unfortunately, there is no out-of-the-box solution regarding implementing a White-Label-Authentication for your users using Auth0 since that level of branding is tenant-wide. That means you would need a multi-tenant environment to handle such a feature. As far as I am concerned, in order for you to accomplish this use case, you would need to be under an Enterprise plan since an Essentials or Professional plan are quite limited. Otherwise, you would need to come up with your own implementation in order to achieve this however you might reach certain limitations or problems.
If you want to know more about a multi-tenant approach, I would advise you to review this community post regarding the matter: Whitelabel within multi tenancy
You can also read more about Embedded login here: Centralized Universal Login vs. Embedded Login
If you have any other questions regarding the matter, feel free to leave a reply and let me know!
Kind Regards,
Nik