diff --git a/src/lib/server/delivery-notes-service.test.ts b/src/lib/server/delivery-notes-service.test.ts
index 2112c69..c5fa4ca 100644
--- a/src/lib/server/delivery-notes-service.test.ts
+++ b/src/lib/server/delivery-notes-service.test.ts
@@ -173,6 +173,7 @@ import {
   markDeliveryNoteInvoiced,
   markDeliveryNoteCompletedByInvoice,
   createAdHocDeliveryNote,
+  updateDeliveryNoteItemPricing,
   generateDeliveryNoteNumberServer,
   getDeliveryNoteDetail,
 } from "./delivery-notes-service";
@@ -658,6 +659,63 @@ describe("generateDeliveryNoteNumberServer", () => {
   });
 });
 
+describe("qty_collected on counter delivery notes", () => {
+  // A counter note is a customer taking goods off the shelf. There is
+  // no driver pickup, so the collection has already happened by the
+  // time the note exists. `qty_collected` is what the invoice path
+  // reads to decide how many units to bill, and leaving it at 0 made
+  // every counter invoice a zero-quantity line, which QuickBooks
+  // rejects (n8n 400 -> an opaque 502 at the operator).
+
+  it("stamps qty_collected = quantity on ad-hoc items at creation", async () => {
+    await createAdHocDeliveryNote({
+      customer: "customer-1",
+      items: [
+        { description: "Husqvarna blower", quantity: 11, cost_price: 100 },
+        { description: "Slideway oil", quantity: 1, cost_price: 50 },
+      ],
+    });
+    const items = [...getOrCreate("order_items").values()] as Array<
+      Record<string, unknown>
+    >;
+    expect(items).toHaveLength(2);
+    for (const item of items) {
+      expect(item.qty_collected).toBe(item.quantity);
+    }
+  });
+
+  it("follows the quantity when a COUNTER note is edited", async () => {
+    // No parent order -> the note quantity IS the collected quantity.
+    seedDeliveryNote({ order: "" });
+    const oiId = seedOrderItem("DN26071401", { order: null, quantity: 10 });
+    await updateDeliveryNoteItemPricing({ itemId: oiId, quantity: 5 });
+    const item = getOrCreate("order_items").get(oiId) as Record<string, unknown>;
+    expect(item.quantity).toBe(5);
+    expect(item.qty_collected).toBe(5);
+  });
+
+  it("leaves an ORDER-linked note's collected qty alone", async () => {
+    // Order-linked notes are owned by the driver pickup flow, where
+    // qty_collected means "in the van". Overwriting it with the order
+    // qty would bill for goods that have not arrived.
+    seedDeliveryNote({ order: "order-1" });
+    const oiId = seedOrderItem("DN26071401", { order: "order-1", quantity: 10 });
+    await updateDeliveryNoteItemPricing({ itemId: oiId, quantity: 5 });
+    const item = getOrCreate("order_items").get(oiId) as Record<string, unknown>;
+    expect(item.quantity).toBe(5);
+    expect(item.qty_collected).toBeUndefined();
+  });
+
+  it("does not touch collected when only the price changes", async () => {
+    seedDeliveryNote({ order: "" });
+    const oiId = seedOrderItem("DN26071401", { order: null, quantity: 10 });
+    await updateDeliveryNoteItemPricing({ itemId: oiId, cost_price: 250 });
+    const item = getOrCreate("order_items").get(oiId) as Record<string, unknown>;
+    expect(item.cost_price).toBe(250);
+    expect(item.qty_collected).toBeUndefined();
+  });
+});
+
 describe("createAdHocDeliveryNote", () => {
   it("creates a delivery_notes header + one order_item per line (no parent order)", async () => {
     const result = await createAdHocDeliveryNote({
diff --git a/src/lib/server/delivery-notes-service.ts b/src/lib/server/delivery-notes-service.ts
index 8d360e2..b5e03ea 100644
--- a/src/lib/server/delivery-notes-service.ts
+++ b/src/lib/server/delivery-notes-service.ts
@@ -1277,6 +1277,18 @@ export async function createAdHocDeliveryNote(
         delivery_note_number: deliveryNoteNumber,
         description: it.description.trim(),
         quantity: Number(it.quantity),
+        // Ad-hoc = counter sale. The customer is standing at the
+        // counter taking the goods, so the collection has ALREADY
+        // happened by the time this row exists — there is no driver
+        // pickup to record. `qty_collected` is what the invoice path
+        // reads to decide how many units to bill, and leaving it 0
+        // produced a zero-quantity invoice line, which QuickBooks
+        // rejects (n8n 400 -> an opaque 502 at the operator).
+        //
+        // "It can even be collected before we even had the system" —
+        // which is exactly the case: nothing here is ever picked up by
+        // a driver, so the note quantity IS the collected quantity.
+        qty_collected: Number(it.quantity),
         supplier: it.supplier ?? null,
         cost_price: Number(it.cost_price ?? 0),
         selling_price:
@@ -2200,6 +2212,21 @@ export async function updateDeliveryNoteItemPricing(
   }
   if (hasQty) patch.quantity = Number(input.quantity);
 
+  // A COUNTER delivery note has no parent order, which means the
+  // goods left the shelf and were handed over — the collection
+  // already happened. `qty_collected` is the field the invoice path
+  // reads to decide how many units to bill, so leaving it at 0 makes
+  // the invoice come out as a zero-quantity line, which QuickBooks
+  // rejects outright (n8n 400, surfaced as an opaque 502).
+  //
+  // Only for parentless notes: an order-linked note is owned by the
+  // driver pickup flow, where `qty_collected` means "the driver has
+  // this many in the van" and overwriting it with the order qty would
+  // bill the customer for goods that have not arrived.
+  if (hasQty && !dn.order) {
+    patch.qty_collected = Number(input.quantity);
+  }
+
   // Stamp the audit tag on every pricing change. Operator-
   // typed values are tagged "manual" so downstream surfaces
   // (process page, sprint rows) can flag it for re-review if