What would it take for a Spherical Earth Believe to accept that the Earth is Flat?
Be honest, their must be something that God could do for you, in order to believe that the earth is Flat
Actual evidence showing Earth is flat. This means that it mustn't be evidence which is compatible with both a flat and round Earth.
As well as a working model which can at least explain several things.
However you could get me to reject Earth being round by pointing out issues with that model, actual issues, not just lies.
Now a question for you akin to what you have asked:
What would it take to convince you that every building in America is made of cheese?
That is like what you are asking for.
There is not a single shred of evidence for the FE model (actually for it, i.e. doesn't work in RE), and there is plenty of evidence against it.
EDIT: Alternatively, what would it take for you to accept Earth is round (i.e. roughly spherical)?