I can’t make an existing outlook account to link to primary hotmail account

I have two existing hotmail accounts, one for personal use and one for business. I have always had them linked, so that the business emails would be forwarded to the personal account, thus saving me from signing in/out all the time.

Perhaps I'm doing this "alias" thing wrong, but when I go to 'Add an existing email address as a Microsoft account alias' I get the following:

Of course it is! The ability to link and forward accounts is the reason I made my business email the same domain as my personal email.

Please tell me there is a way to do this. I just spent a lot of money on new business cards with the other account address!