Sit at a computer (the QR cannot be created in the Google app on a phone) and open your Business Profile. Go to Read reviews, then Get more reviews. Copy the link, or right-click the QR and save the image.
Print it small on the ticket, on the bag, or on a card by the till. One code for the whole business is enough. Do not make a new campaign every week.
The customer scans, lands on Google, and writes if they want. Do not point the QR at a page of yours that first asks “how many stars?” and only then opens Google. That is the same filter as a gated survey.
You do not need WhatsApp for this. Paper does not store a phone number. Use the same QR at lunch and at closing.
If you already send a thank-you by email or message after a booking, you may add the same link there. That is Google’s own list: receipts, thank-you emails, the end of a chat, a printed code in the shop.