Anyone selling food is a food business operator. That includes cloud kitchens, home bakers, packers, transporters and many online sellers. The Food Safety and Standards Act is what asks for the certificate, not the landlord and not Instagram.
Basic registration is only for small operators within the turnover limit. Above it, a state licence or a central licence applies. Manufacturing, storage and multi-state activity push people into a higher licence faster than a single restaurant expects.
Basic registration is mostly identity and address. A state or central licence can ask for a layout, a water report, an equipment list and a responsible person. Filing the cheap form when you need the larger one does not save money; it gets rejected.
Digital Filings starts at INR 1,499/- as a professional fee for the correct application. The FSSAI fee itself depends on the licence and the number of years, and is paid on FoSCoS.