Pen Names - how paid?

Maybe this is a dumb question, but how does one get paid for writing when using a "pen name?" If you write under an alias, and it gets published, to whom does the check get written? Does a writer have to file a business license/DBA ("Doing Business As") in order to legally get paid? Since you normally can't open a bank account with an alias unless it's a Business Name, I've always wondered about this. What if you wanted to write using a pen name but really didn't want anyone to know your true identity? Would an agent safeguard that info? How would you work freelance with an alias?

TIA

When you submit work, you include your legal name in your contact information, on the contract, etc., but on the by-line you list your pseudonym instead of your legal name. The editor may confirm which name you prefer to be published under if he has any doubts.

The agent, editor, accounts payable department, etc. all know who you really are and the check is made out to your legal name, but the readership only sees the by-line.

Are there any restrictions as to what you can use as a pen name. Aside from not using, racial, ethnic, slurs. Swearing, sexual connotations. etc etc