Hi Andrew!
Check out https://apps.shopify.com/jericommerce-admin. You can manually add discounts at the POS with the ShopifyPOS integration, the customer can log in to the online store clicking a link on the wallet with a password-less system (using multipass https://www.jericommerce.com/guides/shopify-multipass-customers-login-automatically), and the customer can also qualify for online discounts and rewards.
Thanks!