Negotiating Pay NBC

So after completing the original brief, nearly in full! NBC have asked me to start the brief again, with the illustrations at a different angle. During the meeting, I had to discuss that I would require seperate payment for my time on the adjustments, as they involve pretty much redoing the entire brief. It was a bit uncomfortable discussing payment with a client, especially being on my own in a boardroom, surrounded by employees of NBC (including the owner) however I was clear and professional in my approach and the offer was accepted.