I have a friend who is in the UK, but an American citizen, and he is trying to get home but has to pay a traveling allowance. Why and What is it?

Who is he paying?

Sorry, NO, you don't have a friend there. You have someone you don't know that contacted you by email. You have someone that promised you something when they get to the US ( sex, love, money)

There is no basic traveling allowance, this is a well known scam.