Make a GST tax invoice

Fields: number (required, up to 16 letters, digits, - and /), date and due_date (YYYY-MM-DD, date defaults to today), title (default Tax Invoice), place_of_supply (state code, name or GST code; defaults to the buyer's state from the GSTIN or state), reverse_charge, seller and buyer (name, address, gstin, state, phone, email; the seller's GSTIN is required), ship_to, items (description, hsn, quantity (default 1), unit (default Nos), rate before tax, discount as an amount, gst_rate in percent), bank (name, account, ifsc, branch, holder), upi, notes and terms. Unknown fields are refused, so a misspelt field is caught. format=json returns the worked-out invoice instead of a document; format=png the first page as a picture.