non-convex collider not colliding

my player falls throught the floor
I created a floor with code.
my player does not fall down from the procedural terrain if i turn on convex(using code).
But I don’t want to use convex.

how to get accurate collider?

I found the answer Mesh Collision from Blender into unity. Easy way. - YouTube

I just have to make an other mesh which is convex and set it to convex