I have request from a lady wanting to buy a voucher for her friend for one night. Her friend will pay the other night. How does this work when the guest needs to pay and also fir the host
I don't think there are vouchers of any kind. Maybe she wants to buy her friend a gift certificate? that wold be done without your involvement.
I would tell that you are happy to host her friend but they will need to work out the financial details out themselves and that after they have done so, they can book like everyone else. Don't offer to "take cash" the second night or anything like that.