new grid for nudging in CAM

[TCNasa]

I found this grid in the components/cam/bld/config_files/horizon_grid.xml file:
0.5x0.625
I'm trying to use some MERRA2 data on that grid for nudging. So I defined this new grid in cime/config/cesm/config_grids.xml file:
<model_grid alias="f51_f51_mg17" not_compset="_POP" >
<grid name="atm">0.5x0.625</grid>
<grid name="lnd">0.5x0.625</grid>
<grid name="ocnice">0.5x0.625</grid>
<mask>gx1v7</mask>
</model_grid>

But I'm still getting some kind of grid undefined error when building:

Calling /CERES/sarb/caldwell/CESM2.2/components/cam//cime_config/buildnml


...calling cam buildcpp to set build time options


ERROR: Command: '/CERES/sarb/caldwell/CESM2.2/components/cam/bld/configure -s -fc_type gnu -dyn fv -hgrid UNSET -cpl mct -usr_src /CERES/sarb/caldwell/CESM2.2/cime/scripts/nudge-test-12/SourceMods/src.cam -spmd -nosmp -ocn docn -phys cam6' failed with error 'set_horiz_grid: no match for dycore fv and hgrid UNSET' from dir '/CERES/sarb/caldwell/CESM2.2/cime/scripts/nudge-test-12/Buildconf/camconf'

where do I need to set some options to get this going?

Thanks.