There is no point in arguing with a "flat earther". Nothing we say or know personally would sway them. What I want to know and find somewhat disturbing is the fact that the flat earth bunch is growing exponentially in number. It is estimated that now up to 1/3 of all millennial's now believe the earth is flat. And yes he truly does not believe that satellites of any kind exist. Yes he believes the sun is some sort of "spotlight" whose rays travel over the surface of the flat earth. Yes he actually believes that. Yes, he believes that the spherical earth is the longest running and largest conspiracy every foisted on mankind.
I see this growth in the number of flat earthers as a form of mental illness. A rejection of technology and learning and an adoption of conspiracy theories as a way of life. Since you and I have now both spoken out in favor of a spherical earth, he probably believes we are part of the "big lie". I pointed out to him that I have talked thru and tracked various Amateur Radio satellites for many years didn't cut any ice with him. He didn't want to hear about Keplarian motions and tracking software. He didn't want to hear about how I upgraded even my first old IBM PC with an 8088 processor by adding a 8087 math co processor so I could calculate the orbits of a particular amateur satellite called OSCAR 10 (Orbital Satellite Carrying Amateur Radio) much faster. He just denied the existence of Amateur Satellites and all satellites for that matter. Even though you can look up and see the largest satellite of all: The moon. He didn't mention what all those other little things you can look at traversing arcs in the night sky are. I don't know how they explain those.
Anyway, I have wrote another "rant" and it won't change a thing in their minds.