(Agency) How do I put all my clients on my agency's domain?

On your agency's own business, click Record page and use Your agency domain (like record.youragency.com). Every client's record page goes on it, like record.youragency.com/clientname. In the same panel you can set Your dashboard address (like app.youragency.com, where your team and clients sign in with your logo) and Your clients' walls (like wall.youragency.com/clientname). Once you have clients, the agency domain can be changed with Change domain but not removed; the current one keeps working until the new one is live, and the old one forwards (you can Stop forwarding later).

For a client, Where this page lives lets you pick On the agency domain or On the client's own domain.