Enhance subscription update preview with quantity checks and billing messages

Author: Bharani0012

src/backend/base/langflow/services/paddle/subscriptions.py

@@ -792,6 +792,8 @@ async def preview_subscription_update(
         paddle_client.subscriptions.get,
         subscription_id,
     )
+    current_quantity = subscription.items[0].quantity
+
     status = str(getattr(subscription, "status", "")).lower()
 
     items = await _build_updated_items(
@@ -815,12 +817,18 @@ async def preview_subscription_update(
 
     plan_price_map = _get_enabled_plan_monthly_price_map()
 
-    proration_mode = _determine_proration_mode(
-        current_plan_key=current_plan_key,
-        new_plan_key=new_plan_key,
-        plan_price_map=plan_price_map,
-        status=status,
-    )
+    if new_quantity > current_quantity and not new_price_id:
+        if status == "trialing":
+            proration_mode = SubscriptionProrationBillingMode.DoNotBill
+        else:
+            proration_mode = SubscriptionProrationBillingMode.ProratedImmediately
+    else:
+        proration_mode = _determine_proration_mode(
+            current_plan_key=current_plan_key,
+            new_plan_key=new_plan_key,
+            plan_price_map=plan_price_map,
+            status=status,
+        )
 
     operation = PreviewUpdateSubscription(
         items=[

src/frontend/src/pages/ChangePlansPage/index.tsx

@@ -26,6 +26,7 @@ type BillingAccessResponse = {
   subscription_seats?: number | null;
   seats?: number | null;
   quantity?: number | null;
+  next_billed_at?: string | null;
 };
 
 type PaddlePricesResponse = Record<string, string>;
@@ -207,6 +208,25 @@ export default function ChangePlansPage() {
     setPendingSeats((prev) => prev + 1);
   };
 
+  function buildPreviewMessage(previewData: any, nextBillingDate?: string): string | null {
+    if (!previewData) return null;
+
+    const hasImmediateCharge = Boolean(previewData?.immediate_transaction);
+    const amount = extractPreviewAmount(previewData);
+
+    if (hasImmediateCharge && amount !== null) {
+      return `You will be charged ${toCurrency(amount)} today.`;
+    }
+
+    if (nextBillingDate) {
+      const date = new Date(nextBillingDate);
+      const formatted = date.toLocaleDateString(undefined, { dateStyle: "medium" });
+      return `Your plan will change on ${formatted}. No charge today.`;
+    }
+
+    return "This change will take effect on your next billing date. No charge today.";
+  }
+
   const handlePlanSelect = async (planKey: string) => {
     if (mode !== "plan" || actionsBlocked || planKey === currentPlanKey) {
       return;
@@ -232,7 +252,7 @@ export default function ChangePlansPage() {
       const amount = extractPreviewAmount(preview);
       setPreviewData(preview);
       setPreviewMessage(
-        amount === null ? null : `You will be charged ${toCurrency(amount)} today.`,
+        buildPreviewMessage(preview, billing?.next_billed_at)
       );
       setSummaryMessage(
         `Plan change: ${currentPlanKey || "current"} → ${planKey} (${currentSeats} seats).`,
@@ -257,7 +277,7 @@ export default function ChangePlansPage() {
         const amount = extractPreviewAmount(preview);
         setPreviewData(preview);
         setPreviewMessage(
-          amount === null ? null : `You will be charged ${toCurrency(amount)} today.`,
+          buildPreviewMessage(preview, billing?.next_billed_at)
         );
       } else {
         const selected = STATIC_PLANS.find((plan) => plan.key === selectedPlanKey);
@@ -275,7 +295,7 @@ export default function ChangePlansPage() {
         const amount = extractPreviewAmount(preview);
         setPreviewData(preview);
         setPreviewMessage(
-          amount === null ? null : `You will be charged ${toCurrency(amount)} today.`,
+          buildPreviewMessage(preview, billing?.next_billed_at)
         );
         setSummaryMessage(
           `Plan change: ${currentPlanKey || "current"} → ${selectedPlanKey} (${currentSeats} seats).`,