JSON — required: merchant, items (each name + price, qty optional). Optional: address, contact, date, reference, currency, subtotal, discount, tax, tip, total, payment, footer.

{
  "merchant": "Rat's Deli",
  "items": [ { "name": "Coffee", "qty": 2, "price": 3.50 } ],
  "tax": 0.78
}

CSV — metadata rows key,value; items item,name,qty,price.

merchant,Rat's Deli
tax,0.78
item,Coffee,2,3.50