The latest draft ordinance in Spain includes technical and functional aspects of the new billing system and fiscalization, with information about QR codes. The QR code must be between 30×30 and 40×40 millimeters in size and contain the URL for information collection or referral service by the recipient of the invoice. The content of the URL includes the NIF (TIN) of the issuer, invoice or receipt details, and the total amount. There are additional rules for QR codes and electronic format invoices or receipts.
Source Fiscal Requirements