fix: send batch sent_at in snake case

.changeset/sweet-ravens-tap.md

@@ -0,0 +1,5 @@
+---
+'pypi/posthog': patch
+---
+
+Send batch `sent_at` using the backend-supported snake_case field.

posthog/request.py

@@ -228,7 +228,7 @@ def post(
     """Post the `kwargs` to the API"""
     log = logging.getLogger("posthog")
     body = kwargs
-    body["sentAt"] = datetime.now(tz=timezone.utc).isoformat()
+    body["sent_at"] = datetime.now(tz=timezone.utc).isoformat()
     trimmed_host = remove_trailing_slash(normalize_host(host))
     url = trimmed_host + cast(str, path)
     body["api_key"] = api_key

posthog/test/test_request.py

@@ -59,6 +59,31 @@ def test_mask_tokens_in_url(url, expected):
     assert _mask_tokens_in_url(url) == expected
 
 
+@pytest.mark.parametrize(
+    "key, expected_present",
+    [
+        ("sent_at", True),
+        ("sentAt", False),
+    ],
+)
+def test_post_sends_snake_case_sent_at(key, expected_present):
+    mock_response = requests.Response()
+    mock_response.status_code = 200
+    mock_session = mock.MagicMock()
+    mock_session.post.return_value = mock_response
+
+    request_module.post(
+        TEST_API_KEY,
+        host="https://test.posthog.com",
+        path="/batch/",
+        session=mock_session,
+        batch=[],
+    )
+
+    data = json.loads(mock_session.post.call_args.kwargs["data"])
+    assert (key in data) is expected_present
+
+
 class TestRequests(unittest.TestCase):
     def test_valid_request(self):
         res = batch_post(