When I try to execute my code I get an error
Failed setting triangles. Some indices are referencing out of bounds vertices. IndexCount: 123, VertexCount: 33
what does it mean?
It means that your triangles array has an integer that is greater than or equal to mesh.vertices.Length.
Each 3 integer set in the triangles array defines which 3 vertices should be used to draw a triangle in your mesh, so each integer in it must be a valid vertices index.