Surface error when I create in grasshopper

[Jeftli_Andiyansah]

anyone can explain why my surface got like this

[John_Brock]

Assigned to Grasshopper category

[wim (Wim Dekeyser)]

Hi Jeftli -

@Jeftli_Andiyansah

anyone can explain why my surface got like this

You are looking at two surfaces right on top of each other. That causes Z-fighting where one surfaces is drawn over the other in some places and the other in other places.
You can either hide the Grasshopper surface or the Rhino surface.
-wim

[Jeftli_Andiyansah]

But how the surface have grid, i do imitate like this photo, grid not showing, just flat surface(red), i do, Set 1 curve to my rectangle, and i connect to surface mesh, and i put number slider, but grid not show

(This photo not my project)

[wim (Wim Dekeyser)]

Use Ctrl+M to turn on mesh edges.
-wim

[Jeftli_Andiyansah]

Nailed it, thanks for your advice