use on_conflict_do_nothing to prevent duplicate insert attempts

app/dao/notifications_dao.py

@@ -1,7 +1,7 @@
 from datetime import timedelta
 
 from flask import current_app
-from sqlalchemy import asc, delete, desc, func, or_, select, text, union, update
+from sqlalchemy import asc, delete, desc, func, insert, or_, select, text, union, update
 from sqlalchemy.orm import joinedload
 from sqlalchemy.orm.exc import NoResultFound
 from sqlalchemy.sql import functions
@@ -71,7 +71,11 @@ def dao_create_notification(notification):
     # notify-api-742 remove phone numbers from db
     notification.to = "1"
     notification.normalised_to = "1"
-    db.session.add(notification)
+    stmt = (
+        insert(Notification).values(notification.serialize()).on_conflict_do_nothing()
+    )
+    db.session.execute(stmt)
+    db.session.commit()
 
 
 def country_records_delivery(phone_prefix):