fix(images): flatten nested image-edit params to SDK multipart form

The openai/azure/compat image-edit funnel merged non_default_params and
extra_body straight into the multipart body, so a nested value (e.g.
extra_body={"metadata": {...}}) reached the httpx encoder and 500'd with
"Invalid type for value. Expected primitive type". Route the funnel through
a shared flattener that serializes nested values as OpenAI-SDK bracket fields
(key[subkey], lists as key[], bools lowercased, None/empty dropped), matching
the wire format of the rest of this fix.

litellm/images/main.py

@@ -19,6 +19,7 @@ from litellm.constants import request_timeout as DEFAULT_REQUEST_TIMEOUT
 from litellm.exceptions import LiteLLMUnknownProvider
 from litellm.litellm_core_utils.litellm_logging import Logging
 from litellm.litellm_core_utils.litellm_logging import Logging as LiteLLMLoggingObj
+from litellm.litellm_core_utils.llm_request_utils import flatten_form_field_values
 from litellm.litellm_core_utils.mock_functions import mock_image_generation
 from litellm.llms.base_llm import BaseImageEditConfig, BaseImageGenerationConfig
 from litellm.llms.custom_httpx.http_handler import AsyncHTTPHandler, HTTPHandler
@@ -851,9 +852,12 @@ def image_edit(
             or custom_llm_provider == "azure"
             or custom_llm_provider in litellm.openai_compatible_providers
         ):
-            image_edit_request_params.update(non_default_params)
-            if isinstance(extra_body, dict):
-                image_edit_request_params.update(extra_body)
+            image_edit_request_params.update(
+                flatten_form_field_values(
+                    non_default_params,
+                    extra_body if isinstance(extra_body, dict) else None,
+                )
+            )
 
         # Pre Call logging
         litellm_logging_obj.update_from_kwargs(

litellm/litellm_core_utils/llm_request_utils.py

@@ -27,6 +27,25 @@ def _flatten_form_field(key: str, value: object) -> tuple[tuple[str, str], ...]:
     return ((key, serialized),)
 
 
+def flatten_form_field_values(*sources: Mapping[str, object] | None) -> tuple[tuple[str, str], ...]:
+    """
+    Flatten JSON-shaped bodies into primitive ``(name, value)`` form fields the
+    way the OpenAI SDK serializes multipart bodies: dicts as ``key[subkey]``,
+    lists as ``key[]``, booleans lowercased, None and empty values dropped.
+    Sources are applied in order, so a later source wins on a key collision when
+    fed to ``dict.update``. Used to funnel provider-specific params into a
+    multipart request without handing the httpx encoder a nested value it
+    rejects with ``Invalid type for value``.
+    """
+    return tuple(
+        pair
+        for source in sources
+        if source is not None
+        for top_key, top_value in source.items()
+        for pair in _flatten_form_field(top_key, top_value)
+    )
+
+
 def serialize_multipart_form_fields(data: Mapping[str, object]) -> tuple[tuple[str, tuple[None, str]], ...]:
     """
     Encode a JSON-shaped body as httpx file-tuples so a request with no file

tests/test_litellm/images/test_image_edit_extra_params.py

@@ -76,6 +76,30 @@ def test_image_edit_extra_body_takes_precedence_over_kwargs():
     assert _multipart_text_fields(captured["content_type"], captured["body"])["seed"] == "7"
 
 
+def test_image_edit_flattens_nested_provider_params():
+    """A nested value in extra_body (or a nested unknown kwarg) must be
+    serialized as OpenAI-SDK bracket form fields (key[subkey]) rather than
+    handed to the httpx multipart encoder, which raises 'Invalid type for
+    value. Expected primitive type' on a dict and 500s the request."""
+    captured = {}
+    client = HTTPHandler(client=httpx.Client(transport=httpx.MockTransport(_capture_image_edit_request(captured))))
+
+    litellm.image_edit(
+        model="openai/gpt-image-1",
+        image=PNG_BYTES,
+        prompt="add a hat",
+        api_key="sk-test",
+        api_base="https://edit.example/v1",
+        client=client,
+        extra_body={"generation_config": {"steps": 30, "guidance": True}},
+    )
+
+    fields = _multipart_text_fields(captured["content_type"], captured["body"])
+    assert fields["generation_config[steps]"] == "30"
+    assert fields["generation_config[guidance]"] == "true"
+    assert "generation_config" not in fields
+
+
 @pytest.mark.asyncio
 async def test_aimage_edit_forwards_extra_body():
     """aimage_edit used to drop extra_headers/extra_query/extra_body when

tests/test_litellm/litellm_core_utils/test_llm_request_utils.py

@@ -1,4 +1,7 @@
-from litellm.litellm_core_utils.llm_request_utils import serialize_multipart_form_fields
+from litellm.litellm_core_utils.llm_request_utils import (
+    flatten_form_field_values,
+    serialize_multipart_form_fields,
+)
 
 
 def test_serialize_multipart_form_fields_flattens_like_the_openai_sdk():
@@ -34,3 +37,28 @@ def test_serialize_multipart_form_fields_drops_empty_strings():
 
 def test_serialize_multipart_form_fields_empty_body():
     assert serialize_multipart_form_fields({}) == ()
+
+
+def test_flatten_form_field_values_flattens_nested_and_drops_empty():
+    assert flatten_form_field_values(
+        {
+            "seed": 42,
+            "hd": True,
+            "size": None,
+            "prompt": "",
+            "generation_config": {"steps": 30, "guidance": True},
+        }
+    ) == (
+        ("seed", "42"),
+        ("hd", "true"),
+        ("generation_config[steps]", "30"),
+        ("generation_config[guidance]", "true"),
+    )
+
+
+def test_flatten_form_field_values_later_source_wins_on_collision():
+    assert flatten_form_field_values({"seed": 1}, None, {"seed": 2}) == (
+        ("seed", "1"),
+        ("seed", "2"),
+    )
+    assert dict(flatten_form_field_values({"seed": 1}, {"seed": 2}))["seed"] == "2"