Nav mesh and 2D tilemaps

I have been trying to get the navigation module to work with tilemaps but I haven’t been able to so far.

I added my tilemap to the level and set it so that it extrudes by 200 units for collisions. I have added a nav mesh bounds volume that contains the tilemap but there is no navigation data being generated (i.e. no green meshes anywhere). What am I doing wrong?