you can import vectosr in SNAP only when a raster is currently opened, at best with a similar (or larger) extent. So, first open a raster product, then you can add the shapefile by selecting the product and then File > Import > Vector
you can import vectosr in SNAP only when a raster is currently opened, at best with a similar (or larger) extent. So, first open a raster product, then you can add the shapefile by selecting the product and then File > Import > Vector