Arrays have incorrect length or dimension. Contour plot in Julia

Question

I am trying to make a simple contour plot.

using Plots

xi = -10:10
zi = 0:-1:-10

X = xi'.*ones(size(zi))
Z = zi .*ones(size(xi))'

plot(contour(X, Z, X, fill = true))

Which returns Arrays have incorrect length or dimension. and an empty figure.

Any idea on what does that means?

size(X),size(Z) returns ((11, 21), (11, 21))