diff --git a/rhodecode/integrations/types/slack.py b/rhodecode/integrations/types/slack.py
--- a/rhodecode/integrations/types/slack.py
+++ b/rhodecode/integrations/types/slack.py
@@ -145,6 +145,10 @@ class SlackIntegrationType(IntegrationTy
 
 @async_task(ignore_result=True, base=RequestContextTask)
 def post_text_to_slack(settings, slack_data: SlackData):
+    # because JSON serialization, if we run async with celery, deserialize to SlackData
+    if isinstance(slack_data, dict):
+        slack_data = SlackData(**slack_data)
+
     title = slack_data.title
     text = slack_data.text
     fields = slack_data.fields
diff --git a/rhodecode/tests/lib/test_ext_json.py b/rhodecode/tests/lib/test_ext_json.py
--- a/rhodecode/tests/lib/test_ext_json.py
+++ b/rhodecode/tests/lib/test_ext_json.py
@@ -1,4 +1,4 @@
-
+import dataclasses
 # Copyright (C) 2010-2023 RhodeCode GmbH
 #
 # This program is free software: you can redistribute it and/or modify
@@ -164,3 +164,15 @@ def test_lazy_translation_string(baseapp
 
     assert b'{"label":"hello"}' == ext_json.json.dumps(data)
     assert b'{"label2":"singular"}' == ext_json.json.dumps(data2)
+
+
+def test_serialize_dataclass():
+
+    @dataclasses.dataclass
+    class ExampleStruct:
+        field_str: str
+        field_int: int
+    struct = ExampleStruct(field_int=1, field_str='hello')
+    raw_struct = b'{"field_str":"hello","field_int":1}'
+    assert raw_struct == ext_json.json.dumps(struct)
+    assert struct == ExampleStruct(**ext_json.json.loads(raw_struct))