JSON — required: seller, items (each name + price, qty optional). Optional: selleraddress, sellercontact, buyer, buyeraddress, buyercontact, invoicenumber, issuedate, duedate, currency, subtotal, discount, tax, taxlabel, total, paymentinstructions, notes.

{
  "seller": "Acme Consulting",
  "buyer": "Client Co",
  "invoicenumber": "INV-2026-001",
  "items": [ { "name": "Consulting hours", "qty": 10, "price": 150 } ],
  "tax": 80
}

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

seller,Acme Consulting
buyer,Client Co
tax,80
item,Consulting hours,10,150