tracing – equation of sine-Gordon using the pseudospectral method

I want to test this code, what is the problem?
I tried this from
https://reference.wolfram.com/language/tutorial/NDSolveMethodOfLines.html
When I tried this I have enter the description of the image here

sol = NDSolve[{D[u[t, x, y], t, t]==
re[u[t, x, y], x, x]+ D[u[t, x, y], and, and]- Sin[u[t, x, y]],
you[0, x, y] == Exp[-(x^2 + y^2)],
Derivative[1, 0, 0][u][0, x, y]    == 0, u[t, -10, y] == u[t, 10, y],
you[t, x, -10] == u[t, x, 10]}
u, {t, 0, 6}, {x, -10, 10}, {y, -10, 10},
Method -> {"MethodOfLines",
"Spatial discretization" -> {"TensorProductGrid",
"DifferenceOrder" -> "Pseudospectral"}}]Plot3D[First[u[6, x, y] /. Sun], {x, 20, 40}, {y, -15, 15},
PlotRange -> All, PlotPoints -> 40]

enter the description of the image here