DreamHost error when trying to add a domain: “You can’t add that domain: you must add the parent domain”

I have hosting account on DreamHost I want to add my domain (which is registered outside Dreamhost) I have already changed nameservers. my domain is "xxxx.edu.eg" but I have the following problem: "You can’t add that domain: you must add the parent domain edu.eg to your account before adding a subdomain to it." How to solve it and thank you in advance