diff --git a/api/handlers/cart.go b/api/handlers/cart.go
index a0a2af3..c9065ca 100644
--- a/api/handlers/cart.go
+++ b/api/handlers/cart.go
@@ -539,9 +539,10 @@ func (h *CartHandler) ConvertCart(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
-// respondRequiresAction handles a PaymentIntent that needs 3DS auth
-// The order stays pending. the webhook flips it to paid once the customer
-// completes the bank-hosted challenge, the tui polls /api/v1/orders/{id}/status
+// respondRequiresAction handles a PaymentIntent that needs 3DS auth. The order
+// transitions to requires_action (see caveat #20 in sca-psd2-compliance.md);
+// the payment_intent.succeeded webhook flips it to paid once the customer
+// completes the bank-hosted challenge. The TUI polls /api/v1/orders/{id}/status.
 func (h *CartHandler) respondRequiresAction(w http.ResponseWriter, order *models.Order, paymentMethodID string, pi *stripe.PaymentIntent) {
 	db := database.GetDB()
 
diff --git a/api/handlers/cart_test.go b/api/handlers/cart_test.go
index 446c838..52d5795 100644
--- a/api/handlers/cart_test.go
+++ b/api/handlers/cart_test.go
@@ -921,7 +921,7 @@ func TestRetryAuth(t *testing.T) {
 			wantStatus: http.StatusConflict, wantErrCode: "INVALID_STATE",
 		},
 		{
-			name:        "requires_action retryable until cap",
+			name:        "requires_action honors retry cap",
 			ownedByUser: true, seedStatus: models.OrderStatusRequiresAction,
 			seedPayment: "pi_test_req_action_cap", seedEvents: maxAuthIssuances,
 			wantStatus: http.StatusTooManyRequests, wantErrCode: "RETRY_LIMIT",
diff --git a/api/handlers/webhook_test.go b/api/handlers/webhook_test.go
index e299305..988202a 100644
--- a/api/handlers/webhook_test.go
+++ b/api/handlers/webhook_test.go
@@ -185,3 +185,40 @@ func TestHandlePaymentIntentFailed_MissingMetadataNoOp(t *testing.T) {
 	h := NewWebhookHandler("", "", "")
 	h.handlePaymentIntentFailed(context.Background(), evt) // must not panic
 }
+
+func TestHandlePaymentIntentSucceeded_RequiresActionFlipsToPaid(t *testing.T) {
+	testDB, user := setupCartTestDB(t)
+	defer func() { _ = os.Remove(testDB) }()
+	defer database.ResetForTesting()
+
+	order := seedOrderForWebhook(t, user.ID, models.OrderStatusRequiresAction, "pi_test_req_action_paid")
+
+	pi := map[string]any{
+		"id":       order.StripePaymentID,
+		"amount":   order.Total,
+		"metadata": map[string]string{"order_id": fmt.Sprintf("%d", order.ID)},
+	}
+	raw, err := json.Marshal(pi)
+	if err != nil {
+		t.Fatalf("marshal pi: %v", err)
+	}
+	evt := stripe.Event{
+		Type: "payment_intent.succeeded",
+		Data: &stripe.EventData{Raw: raw},
+	}
+
+	h := NewWebhookHandler("", "", "")
+	h.handlePaymentIntentSucceeded(context.Background(), evt)
+
+	db := database.GetDB()
+	var reloaded models.Order
+	if err := db.First(&reloaded, order.ID).Error; err != nil {
+		t.Fatalf("reload order: %v", err)
+	}
+	if reloaded.Status != models.OrderStatusPaid {
+		t.Fatalf("status: want %q, got %q", models.OrderStatusPaid, reloaded.Status)
+	}
+	if reloaded.StripePaymentID != order.StripePaymentID {
+		t.Fatalf("stripe_payment_id: want %q, got %q", order.StripePaymentID, reloaded.StripePaymentID)
+	}
+}