error:[Nodeld: Back-Geocoding] same sub-swath is expected snap,

BackGeocoding allows to coregister SLC products at sub-pixel accuracy, e.g. for interfefrometric analyses. These work only on images acquired from the same track (explained here).

If you want to use information of products of different tracks, you have to geocode them first (Range Doppler Terrain Correction). If you don’t need the phase information, GRD products are sufficient.