diff --git a/backend/postcode_splitter/main.py b/backend/postcode_splitter/main.py
index e49a7f0d..b3c78b20 100644
--- a/backend/postcode_splitter/main.py
+++ b/backend/postcode_splitter/main.py
@@ -5,7 +5,11 @@ import pandas as pd
 import requests
 import boto3
 from uuid import UUID, uuid4
-from utils.s3 import read_csv_from_s3 as read_csv_from_s3_dict, save_csv_to_s3, parse_s3_uri
+from utils.s3 import (
+    read_csv_from_s3 as read_csv_from_s3_dict,
+    save_csv_to_s3,
+    parse_s3_uri,
+)
 from utils.logger import setup_logger
 from tqdm import tqdm
 from backend.app.db.functions.tasks.Tasks import SubTaskInterface
@@ -136,7 +140,7 @@ def create_batch_and_send_to_address2uprn(
     # Send message with S3 reference
     send_to_address2uprn_queue(
         task_id=str(task_id),
-        sub_task_id=created_batch_sub_task_id,
+        sub_task_id=str(created_batch_sub_task_id),
         s3_uri=s3_uri,
     )