diff --git a/src/aleph/chains/chain_data_service.py b/src/aleph/chains/chain_data_service.py
index 219a01d8..2e83c2b1 100644
--- a/src/aleph/chains/chain_data_service.py
+++ b/src/aleph/chains/chain_data_service.py
@@ -1,4 +1,5 @@
 import asyncio
+import json
 from typing import Any, Dict, List, Mapping, Optional, Self, Set, Type, Union, cast
 
 import aio_pika.abc
@@ -191,7 +192,7 @@ def _get_tx_messages_smart_contract_protocol(tx: ChainTxDb) -> List[Dict[str, An
                 item_hash=ItemHash(payload.content),
                 metadata=None,
             )
-            item_content = content.model_dump_json(exclude_none=True)
+            item_content = json.dumps(content.model_dump(exclude_none=True))
         else:
             item_content = payload.content
 
diff --git a/tests/api/test_balance.py b/tests/api/test_balance.py
index c37d1b44..2064ed8a 100644
--- a/tests/api/test_balance.py
+++ b/tests/api/test_balance.py
@@ -23,5 +23,5 @@ async def test_get_balance(
     response = await ccn_api_client.get(MESSAGES_URI)
     assert response.status == 200, await response.text()
     data = await response.json()
-    assert data["balance"] == user_balance.balance
-    assert data["locked_amount"] == 2002.4666666666667
+    assert data["balance"] == str(user_balance.balance)
+    assert data["locked_amount"] == '2002.4666666666667'
diff --git a/tests/api/test_list_messages.py b/tests/api/test_list_messages.py
index 2659387b..b191e3a7 100644
--- a/tests/api/test_list_messages.py
+++ b/tests/api/test_list_messages.py
@@ -70,9 +70,7 @@ async def test_get_messages(fixture_messages: Sequence[Dict[str, Any]], ccn_api_
 @pytest.mark.asyncio
 async def test_get_messages_filter_by_channel(fixture_messages, ccn_api_client):
     async def fetch_messages_by_channel(channel: str) -> Dict:
-        response = await ccn_api_client.get(
-            MESSAGES_URI, params={"channels": channel}
-        )
+        response = await ccn_api_client.get(MESSAGES_URI, params={"channels": channel})
         assert response.status == 200, await response.text()
         return await response.json()
 
@@ -194,9 +192,7 @@ async def test_get_messages_filter_by_tags(
     assert len(messages) == 2
 
     # Matching tags for both messages
-    response = await ccn_api_client.get(
-        MESSAGES_URI, params={"tags": "original,amend"}
-    )
+    response = await ccn_api_client.get(MESSAGES_URI, params={"tags": "original,amend"})
     assert response.status == 200, await response.text()
     messages = (await response.json())["messages"]
     assert len(messages) == 2
diff --git a/tests/api/test_posts.py b/tests/api/test_posts.py
index b63cb770..bd0e7b44 100644
--- a/tests/api/test_posts.py
+++ b/tests/api/test_posts.py
@@ -261,9 +261,7 @@ async def test_get_amended_posts_tags(
         session.commit()
 
     # Match one tag
-    response = await ccn_api_client.get(
-        "/api/v0/posts.json", params={"tags": "amend"}
-    )
+    response = await ccn_api_client.get("/api/v0/posts.json", params={"tags": "amend"})
     assert response.status == 200
     response_json = await response.json()
     assert len(response_json["posts"]) == 1
diff --git a/tests/chains/test_chain_data_service.py b/tests/chains/test_chain_data_service.py
index b41c0bf5..722d8573 100644
--- a/tests/chains/test_chain_data_service.py
+++ b/tests/chains/test_chain_data_service.py
@@ -1,4 +1,5 @@
 import datetime as dt
+import json
 
 import pytest
 from aleph_message.models import (
@@ -135,7 +136,7 @@ async def test_smart_contract_protocol_regular_message(
         timestamp=1668611900,
         addr="KT1VBeLD7hzKpj17aRJ3Kc6QQFeikCEXi7W6",
         msgtype="POST",
-        msgcontent=content.json(),
+        msgcontent=json.dumps(content.model_dump()),
     )
 
     tx = ChainTxDb(
@@ -146,7 +147,7 @@ async def test_smart_contract_protocol_regular_message(
         publisher="KT1BfL57oZfptdtMFZ9LNakEPvuPPA2urdSW",
         protocol=ChainSyncProtocol.SMART_CONTRACT,
         protocol_version=1,
-        content=payload.model_dump(),
+        content=payload.model_dump(mode="json"),
     )
 
     chain_data_service = ChainDataService(