diff --git a/autogpt_platform/backend/backend/data/credit.py b/autogpt_platform/backend/backend/data/credit.py
index ae730aa81c..ee21b907db 100644
--- a/autogpt_platform/backend/backend/data/credit.py
+++ b/autogpt_platform/backend/backend/data/credit.py
@@ -1716,6 +1716,9 @@ async def handle_subscription_payment_failure(invoice: dict) -> None:
             amount=-amount_due,
             transaction_type=CreditTransactionType.SUBSCRIPTION,
             fail_insufficient_credits=True,
+            # Use invoice_id as the idempotency key so that Stripe webhook retries
+            # (e.g. on a transient stripe.Invoice.pay failure) do not double-charge.
+            transaction_key=invoice_id or None,
             metadata=SafeJson(
                 {
                     "stripe_customer_id": customer_id,
diff --git a/autogpt_platform/backend/backend/data/credit_subscription_test.py b/autogpt_platform/backend/backend/data/credit_subscription_test.py
index 5192cda04e..8a9666b87f 100644
--- a/autogpt_platform/backend/backend/data/credit_subscription_test.py
+++ b/autogpt_platform/backend/backend/data/credit_subscription_test.py
@@ -988,3 +988,31 @@ async def test_handle_subscription_payment_failure_invoice_pay_error_does_not_ra
     ):
         # Must not raise — the pay failure is only logged as a warning
         await handle_subscription_payment_failure(invoice)
+
+
+@pytest.mark.asyncio
+async def test_handle_subscription_payment_failure_passes_invoice_id_as_transaction_key():
+    """invoice_id is used as the idempotency key to prevent double-charging on webhook retries."""
+    mock_user = _make_user(user_id="user-1", tier=SubscriptionTier.PRO)
+    invoice = {
+        "id": "in_idempotency_test",
+        "customer": "cus_123",
+        "subscription": "sub_abc123",
+        "amount_due": 2000,
+    }
+
+    with (
+        patch(
+            "backend.data.credit.User.prisma",
+            return_value=MagicMock(find_first=AsyncMock(return_value=mock_user)),
+        ),
+        patch(
+            "backend.data.credit.UserCredit._add_transaction",
+            new_callable=AsyncMock,
+        ) as mock_add_tx,
+        patch("backend.data.credit.stripe.Invoice.pay"),
+    ):
+        await handle_subscription_payment_failure(invoice)
+        mock_add_tx.assert_called_once()
+        _, kwargs = mock_add_tx.call_args
+        assert kwargs.get("transaction_key") == "in_idempotency_test"