Yes — the proposal checkout is a full Sprwt checkout. The customer can enter a gift-card/coupon code (Apply), tick Use Digital Balance to spend store credit first (the remainder goes to the card), and choose a gratuity from the tip buttons (No Tip, up to the first two preset amounts configured in Tips - Values plus a custom Other amount, using Tips - Type — Percentage or Fixed — from Business: Cart). Discounts and tips are only applied when the customer pays the full balance now: choosing Pay Later (a deposit) zeroes out both the tip and any coupon on that payment, so a deposit can't be discounted or tipped. You can also apply these on the customer's behalf from the admin Make Payment window.