Points now subtract from costs

backend/src/main/java/com/petshop/backend/controller/CartController.java

@@ -75,6 +75,16 @@ public class CartController {
         return ResponseEntity.ok(cartService.applyCoupon(userId, storeId, request.getCouponCode()));
     }
 
+    @PostMapping("/apply-points")
+    @PreAuthorize("isAuthenticated()")
+    public ResponseEntity<CartResponse> applyPoints(
+            @RequestParam Long storeId,
+            @RequestParam Boolean useLoyaltyPoints) {
+        Long userId = AuthenticationHelper.getAuthenticatedUserId();
+
+        return ResponseEntity.ok(cartService.applyPoints(userId, storeId, useLoyaltyPoints));
+    }
+
     @DeleteMapping("/coupon")
     @PreAuthorize("isAuthenticated()")
     public ResponseEntity<CartResponse> removeCoupon(@RequestParam Long storeId) {

backend/src/main/java/com/petshop/backend/service/CartService.java

@@ -257,6 +257,34 @@ public class CartService {
                 .setScale(0, RoundingMode.HALF_UP)
                 .longValue();
 
+        // Free checkout: total is $0.00, or points are applied and the remaining
+        // amount is below Stripe's $0.50 minimum (cannot be charged via card)
+        if (amountInCents == 0 || (amountInCents < 50 && Boolean.TRUE.equals(cart.getPointsApplied()))) {
+            SaleRequest saleRequest = new SaleRequest();
+            saleRequest.setStoreId(cart.getStore().getStoreId());
+            saleRequest.setCustomerId(cart.getUser().getId());
+            saleRequest.setCartId(cart.getCartId());
+            saleRequest.setCouponId(cart.getCoupon() != null ? cart.getCoupon().getCouponId() : null);
+            saleRequest.setPaymentMethod("Points");
+            saleRequest.setChannel("WEBSITE");
+            saleRequest.setItems(items.stream()
+                    .map(item -> {
+                        SaleItemRequest sir = new SaleItemRequest();
+                        sir.setProdId(item.getProduct().getProdId());
+                        sir.setQuantity(item.getQuantity());
+                        return sir;
+                    })
+                    .toList());
+
+            saleService.createSale(saleRequest);
+
+            cart.setCartStatus("CHECKED_OUT");
+            cart.setCheckoutPending(false);
+            cartRepository.save(cart);
+
+            return new CheckoutResponse(cart.getCartId(), null, BigDecimal.ZERO, "succeeded");
+        }
+
         if (amountInCents < 50) {
             throw new BusinessException("Order total is too low to process payment");
         }
@@ -489,10 +517,12 @@ public class CartService {
             return BigDecimal.ZERO;
         }
 
-        BigDecimal maxRedeemable = remainingAmount.setScale(0, RoundingMode.DOWN);
-        return BigDecimal.valueOf(wholeDollars)
-                .min(maxRedeemable)
-                .setScale(2, RoundingMode.HALF_UP);
+        BigDecimal maxDiscount = BigDecimal.valueOf(wholeDollars);
+        // If points can fully cover the remaining amount, discount the entire total to $0.00
+        if (maxDiscount.compareTo(remainingAmount) >= 0) {
+            return remainingAmount.setScale(2, RoundingMode.HALF_UP);
+        }
+        return maxDiscount.setScale(2, RoundingMode.HALF_UP);
     }
 
     private CartResponse toResponse(Cart cart) {