Nepalis are free to enter India for shopping (cheaper than in Nepal). So are Indians, no visa is needed to cross the border. There is simply no checkpoint.
This reminded me my experience entering Hong Kong from Shenzhen. Although both belong to the same country, I had to go pass through Mainland border control, Mainland customs, Hong Kong border control, and Hong Kong customs, totally four stops.
India provides lots of aids to Nepal. Some infrastructures along my trekking route were aided by India.