Redirect Driving Me Crazy

Hi Folks Seriously hope this isn't a duplicate of many other queries and apologise if it is. I am constantly having to recreate a redirect for a client's website to another provider. He has a Wordpress website on my server called domaina.com but he no longer wants it to display when folks visit domaina.com. He wants it to instead redirect to domainb.com which is hosted elsewhere. I set up the redirect and it appears to work fine for a while but (perhaps when CRON runs I don't know) eventually fails and people just get a directory listing when browsing to domaina.com. It's driving me (and of course my client) crazy. Can someone please tell me what I'm doing that's obviously not correct? 1. I go to domains/redirects in the client cPanel 2. I select permanent 301 3. I drop down the https and select domaina.com 4. I leave the "/" as default 5. I enter the full URL for the redirect