microsoft/semantic-kernel · error · FunctionExecutionException

This `RestApiPayload` instance is frozen and cannot be modif

Error message

This `RestApiPayload` instance is frozen and cannot be modified.

What it means

`RestApiPayload._throw_if_frozen` raises `FunctionExecutionException` if any setter is invoked after `freeze()` set `_is_frozen = True`. Because `freeze()` also calls `property.freeze()` on every nested property, the whole payload tree becomes immutable once an owning operation is frozen after REST-function registration.

Source

Thrown at python/semantic_kernel/connectors/openapi_plugin/models/rest_api_payload.py:37

        schema: str | None = None,
    ):
        """Initialize the RestApiPayload."""
        self._media_type = media_type
        self._properties = properties
        self._description = description
        self._schema = schema
        self._is_frozen = False

    def freeze(self):
        """Make the instance immutable and freeze properties."""
        self._is_frozen = True
        for property in self._properties:
            property.freeze()

    def _throw_if_frozen(self):
        """Raise an exception if the object is frozen."""
        if self._is_frozen:
            raise FunctionExecutionException("This `RestApiPayload` instance is frozen and cannot be modified.")

    @property
    def media_type(self):
        """Get the media type of the payload."""
        return self._media_type

    @media_type.setter
    def media_type(self, value: str):
        self._throw_if_frozen()
        self._media_type = value

    @property
    def description(self):
        """Get the description of the payload."""
        return self._description

    @description.setter
    def description(self, value: str | None):

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Edit the source OpenAPI spec and re-run `create_functions_from_openapi` so a fresh (unfrozen) payload is built.
2. Construct a new `RestApiPayload(...)` with the desired fields and assign it before registration.
3. Perform any payload mutation prior to the `operation.freeze()` call in the registration pipeline.
4. Avoid reusing a payload object across multiple registered operations.

Example fix

// before
kernel.add_openapi_plugin(...)
operation.payload.media_type = "application/xml"  # raises 1481

// after
spec["paths"]["/x"]["post"]["requestBody"]["content"] = {"application/xml": {...}}
kernel.add_openapi_plugin_from_spec(spec, ...)

def assert_payload_mutable(payload) -> None:
    if getattr(payload, "_is_frozen", False):
        raise RuntimeError("RestApiPayload is frozen; reconstruct it instead.")

assert_payload_mutable(operation.payload)

def is_unfrozen_payload(obj) -> bool:
    return hasattr(obj, "_is_frozen") and not obj._is_frozen

from semantic_kernel.exceptions import FunctionExecutionException

try:
    operation.payload.media_type = "application/json"
except FunctionExecutionException as e:
    if "frozen" in str(e):
        # rebuild from spec instead
        raise RuntimeError("Re-parse the spec to change payload media type") from e
    raise

When it happens

Trigger: Setting `media_type` or any other payload property after the operation owning the payload has been frozen. The freeze cascade is triggered by `RestApiOperation.freeze()` (called at the end of `_create_rest_api_operation` registration in `create_rest_api_operations` / inside `create_functions_from_openapi`).

Common situations: Editing `operation.payload` (e.g. swapping the media type or rewriting properties) after the plugin was already added to the kernel; sharing a parsed operation between two kernel functions and mutating it for the second one; test code that post-processes parsed payloads.

Related errors

• This `RestApiParameter` instance is frozen and cannot be mod
• This instance is frozen and cannot be modified.
• The `RestApiOperation` instance with id {self.id} is frozen
• Invalid server_url_override: {self.server_url_override}
• Either `openapi_document_path` or `openapi_parsed_spec` must

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/65c14d6b8b9b87ed. Report an issue: GitHub.