QRify does not require you to download a special app. If the type of the QR code that you are generating is "Fatoora" QR - you must use ZATCA's app (or a similar one) that knows how to read the special QR code of the Fatoora (which is not a regular QR code).
Let us know if you have any more questions - we have a chat and email support in the app's dashboard :)
