Removed for rule 1 violations. Argument:

the stars and constellations are different in Australia vs. USA which is impossible if we are all on a flat plane looking up. You claim to have a friend on the east coast and you are in europe, so

Measure Polaris from two latitudes. The simplest way to get astronomic latitude in the Northern Hemisphere is to measure the elevation of Polaris above the horizon. In plain English: as you move north, Polaris rises by the same number of degrees as your latitude increases. On a curved Earth, that is exactly what should happen because your local “up” direction tilts as you move over the surface. If Earth were a flat plane, you would not get that clean latitude match over large distances.

BTW, the chances of you sending me $1000 are zero. You also claim you have mathematical evidence which (you haven't posted, mod added)

Removed for rule 1 violations. Argument:

the stars and constellations are different in Australia vs. USA which is impossible if we are all on a flat plane looking up. You claim to have a friend on the east coast and you are in europe, so

Measure Polaris from two latitudes. The simplest way to get astronomic latitude in the Northern Hemisphere is to measure the elevation of Polaris above the horizon. In plain English: as you move north, Polaris rises by the same number of degrees as your latitude increases. On a curved Earth, that is exactly what should happen because your local “up” direction tilts as you move over the surface. If Earth were a flat plane, you would not get that clean latitude match over large distances.

BTW, the chances of you sending me $1000 are zero. You also claim you have mathematical evidence which (you haven't posted)