Fix: prevent duplicate payment enqueuing if all celery workers are stuck

api/management/commands/follow_invoices.py

@@ -184,6 +184,8 @@ def send_ln_payments(self):
                 order.trade_escrow.status == LNPayment.Status.SETLED
                 and order.is_swap is False
             ):
+                lnpayment.status = LNPayment.Status.QUEUED
+                lnpayment.save(update_fields=["status"])
                 follow_send_payment.delay(lnpayment.payment_hash)
 
     def send_onchain_payments(self):

api/migrations/0058_alter_lnpayment_status.py

@@ -0,0 +1,18 @@
+# Generated by Django 5.2.17 on 2026-08-19 02:34
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0057_robot_webhook_enabled_alter_order_escrow_duration'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='lnpayment',
+            name='status',
+            field=models.PositiveSmallIntegerField(choices=[(0, 'Generated'), (1, 'Locked'), (2, 'Settled'), (3, 'Returned'), (4, 'Cancelled'), (5, 'Expired'), (6, 'Valid'), (7, 'In flight'), (8, 'Succeeded'), (9, 'Routing failed'), (10, 'Queued')], default=0),
+        ),
+    ]

api/models/ln_payment.py

@@ -30,6 +30,7 @@ class Status(models.IntegerChoices):
         FLIGHT = 7, "In flight"
         SUCCED = 8, "Succeeded"
         FAILRO = 9, "Routing failed"
+        QUEUED = 10, "Queued"
 
     class FailureReason(models.IntegerChoices):
         NOTYETF = 0, "Payment isn't failed (yet)"

api/tests/test_follow_invoices.py

@@ -0,0 +1,81 @@
+from datetime import timedelta
+from unittest.mock import patch
+from django.test import TestCase
+from django.contrib.auth.models import User
+from django.utils import timezone
+from api.models import LNPayment, Order
+from api.management.commands.follow_invoices import Command
+
+
+class TestFollowInvoices(TestCase):
+    def setUp(self):
+        self.user = User.objects.create_user(username="maker", password="password")
+        self.escrow_user = User.objects.create_user(username="escrow", password="password")
+
+        now = timezone.now()
+        # Create escrow payment with SETLED status
+        self.escrow_payment = LNPayment.objects.create(
+            payment_hash="abc123escrow",
+            type=LNPayment.Types.HOLD,
+            concept=LNPayment.Concepts.TRESCROW,
+            status=LNPayment.Status.SETLED,
+            num_satoshis=100000,
+            sender=self.user,
+            receiver=self.escrow_user,
+            created_at=now,
+            expires_at=now + timedelta(hours=1),
+        )
+
+        # Create payout payment (norm type, FLIGHT status)
+        self.payout_payment = LNPayment.objects.create(
+            payment_hash="abc123payout",
+            type=LNPayment.Types.NORM,
+            concept=LNPayment.Concepts.PAYBUYER,
+            status=LNPayment.Status.FLIGHT,
+            num_satoshis=99000,
+            sender=self.escrow_user,
+            receiver=self.user,
+            created_at=now,
+            expires_at=now + timedelta(hours=1),
+        )
+
+        # Create order linking escrow and payout
+        self.order = Order.objects.create(
+            maker=self.user,
+            trade_escrow=self.escrow_payment,
+            payout=self.payout_payment,
+            is_swap=False,
+            type=Order.Types.BUY,
+            expires_at=now + timedelta(hours=1),
+        )
+
+    @patch("api.management.commands.follow_invoices.follow_send_payment")
+    def test_send_ln_payments_queues_once(self, mock_follow_send_payment):
+        """
+        Validates that send_ln_payments enqueues the payment once and updates
+        its status to QUEUED, preventing duplicate enqueuing on subsequent polls
+        (which would happen in main where status remained FLIGHT).
+        """
+        command = Command()
+
+        # First run of send_ln_payments
+        command.send_ln_payments()
+
+        # Verify task was called once
+        mock_follow_send_payment.delay.assert_called_once_with(self.payout_payment.payment_hash)
+
+        # Verify payment status changed to QUEUED
+        self.payout_payment.refresh_from_db()
+        if hasattr(LNPayment.Status, "QUEUED"):
+            self.assertEqual(self.payout_payment.status, LNPayment.Status.QUEUED)
+        else:
+            # If QUEUED status is not defined, we can skip this assertion
+            pass 
+
+        # Second run of send_ln_payments (simulating subsequent poll when workers are stuck)
+        mock_follow_send_payment.reset_mock()
+        command.send_ln_payments()
+
+        # Verify task was NOT called again (only enqueued once)
+        mock_follow_send_payment.delay.assert_not_called()
+