microsoft/semantic-kernel · error · AgentInvokeException

Function call is expected but not found in the response.

Error message

Function call is expected but not found in the response.

What it means

Raised by _handle_return_control_event when parse_return_control_payload returns an empty list. parse_return_control_payload iterates over return_control_payload.get('invocationInputs', []); if invocationInputs is missing or empty, no FunctionCallContent objects are produced, yet the event was classified as a RETURN_CONTROL event, which is contradictory.

Source

Thrown at python/semantic_kernel/agents/bedrock/bedrock_agent.py:577

            role=AuthorRole.ASSISTANT,
            content=completion,
            name=self.name,
            inner_content=event,
            ai_model_id=self.agent_model.foundation_model,
            metadata=chunk,
        )

    async def _handle_return_control_event(
        self,
        event: dict[str, Any],
        kernel: Kernel,
        kernel_arguments: KernelArguments,
    ) -> dict[str, Any]:
        """Handle return control event."""
        return_control_payload = event[BedrockAgentEventType.RETURN_CONTROL]
        function_calls = parse_return_control_payload(return_control_payload)
        if not function_calls:
            raise AgentInvokeException("Function call is expected but not found in the response.")

        function_result_contents = await self._handle_function_call_contents(function_calls)

        return {
            "invocationId": function_calls[0].id,
            "returnControlInvocationResults": parse_function_result_contents(function_result_contents),
        }

    def _handle_files_event(self, event: dict[str, Any]) -> list[BinaryContent]:
        """Handle file event."""
        files_event = event[BedrockAgentEventType.FILES]
        return [
            BinaryContent(
                data=file["bytes"],
                data_format="base64",
                mime_type=file["type"],
                metadata={"name": self._sanitize_filename(file["name"])},
            )

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Inspect the raw return_control_payload event to verify whether invocationInputs is present and populated.
2. Verify the kernel function action group was created successfully and the function schema is registered with the agent.
3. Re-create the agent's action group via create_kernel_function_action_group to ensure the schema is attached.
4. If the issue is transient, retry the invocation; if persistent, check the Bedrock agent configuration in the AWS console.

Example fix

// before
# event = {'returnControl': {'invocationId': 'x', 'invocationInputs': []}}
# -> raises Function call is expected but not found

// after
# Debug before raising:
raw = await agent._invoke_agent(thread.id, "test")
for ev in raw.get('completion', []):
    if 'returnControl' in ev:
        print(ev['returnControl'].get('invocationInputs'))  # inspect
# Then re-create the action group to fix schema registration

from semantic_kernel.exceptions.agent_exceptions import AgentInvokeException

try:
    resp = await agent.get_response(message=msg, thread=thread)
except AgentInvokeException as e:
    if "Function call is expected but not found" in str(e):
        # re-create the action group to ensure function schema is registered
        await agent.create_kernel_function_action_group()
        resp = await agent.get_response(message=msg, thread=thread)
    else:
        raise

When it happens

Trigger: Triggered when an event contains a 'returnControl' key but its payload has no 'invocationInputs' (or an empty list), so parse_return_control_payload yields [].

Common situations: The Bedrock service sent a malformed or empty RETURN_CONTROL event; the agent's action group/function schema is misconfigured so no function invocation input is included; an API version mismatch changes the payload shape; a race condition or partial response.

Related errors

• No function results were returned.
• Type {type_} is not allowed in bedrock function parameter ty
• Chat message content is expected but not found in the respon
• No response from the agent.
• Failed to get a response from the agent. Please consider inc

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/ae97e1c4ab69a0de. Report an issue: GitHub.