I have written some shaders as text and saved them in vfl files. Then I compile them into a otl files called shaders.otl.
Now I want to use these shaders in a mantra ifd file for rendering, but I'm unsure how to use them. I added a path to the otl in the ifd file:
ray_loadotl cmantra/project/shaders/shaders.otl
Then later in the ifd file, I try to use the shader like this:

ray_start object
ray_transform 17.980289 0 0 0 0 17.980289 0 0 0 0 17.980289 0 0 0 0 1
ray_geometry /meshes/plane
ray_property object surface simpleLambert_surface
ray_property object name “plane”
ray_end


Of course this does not work, I get an error:

mantra: VEX error: Unable to open simpleLambert_surface.vex Path not found
mantra: VEX error: Unable to load simpleLambert_surface Path not found


I think I'm not familiar enough with the correct implementation of shaders and surfaces in houdini, so any hint how I can make my shader work or whre I can find more information would be appreciated.
I was able to import my otl into mantra as new library. There I can create a new shop/surface node and there it appears in “digtal assets”. If I then create a shop node, I can assign and render from within houdini and the result looks promising. But I'd like to avoid this procedure if possible and use the shader directly in the ifd file.