Keeping the link after the sale
A satisfied customer is your best acquisition channel. But you must keep the link. An email reminder has a low click rate, an SMS is quickly forgotten, and app notifications require an installed app.
A physical object left at the customer's stays visible for months. Magnet on the fridge, keyring on the keychain, card in the wallet. When the customer has a need, they scan the object and arrive on the right page.