When does the customer see the UPI QR code to pay?

The QR code is shown after the order is placed, not on the checkout page. At checkout the customer picks UPI and sees a note that the QR will appear on the next page.

On the order confirmation page they get:

• the QR code, made automatically from your UPI ID, so no image upload is needed
• your UPI ID and, on phones, a link to open their UPI app
• your Instructions text
• a form to submit their payment reference

For orders in INR, the order amount is filled into the QR, so the customer doesn't have to type it. The order stays Pending until you confirm the payment.