diff --git a/app/celery/service_callback_tasks.py b/app/celery/service_callback_tasks.py
index 52d86f631..4dfe0c953 100644
--- a/app/celery/service_callback_tasks.py
+++ b/app/celery/service_callback_tasks.py
@@ -3,6 +3,7 @@ import json
 from notifications_utils.statsd_decorators import statsd
 
 from app import (
+    db,
     DATETIME_FORMAT,
     notify_celery,
 )
@@ -30,6 +31,9 @@ def send_delivery_status_to_service(self, notification_id):
         # No delivery receipt API info set
         return
 
+    # Release DB connection before performing an external HTTP request
+    db.session.close()
+
     data = {
         "id": str(notification_id),
         "reference": str(notification.client_reference),