I am trying to test the "payload" human in the loop feature. Below is my code.

from google.adk import Agent
from google.adk.apps import App
from google.adk.apps import ResumabilityConfig
from google.adk.tools.tool_context import ToolContext
from dotenv import load_dotenv

load_dotenv()


def get_user_name(tool_context : ToolContext) -> str:
    tool_confirmation = tool_context.tool_confirmation
    if not tool_confirmation :
        tool_context.request_confirmation(
            hint=('Please approve or reject the tool call get_user_name() by'
            ' responding with a FunctionResponse with an expected'
            ' ToolConfirmation payload.'
            ),
            payload={'user_name': 'user'},  # placeholder for user name
        )

        return {'status': 'Waiting for user to provide their name.'}
    print(tool_confirmation.payload)
    # Get confirmation details
    user_name = tool_confirmation.payload['user_name']

    return {
        'status': 'success',
        'user_name': user_name
    } 


participant_hitl_agent = Agent(
    name="participant_hitl_agent",
    model="gemini-2.5-flash",
    description="The Participant HITL Agent will ask user for their name and store in the the state variables.",
    instruction="""
    You are the participant HITL agent of 'Who Wants to Be a Millionaire.'
    Your task is to ask the user for their name using the `get_user_name` tool.
    IMPORTANT: DO NOT return JSON until AFTER the user gives their name.
    Once you get it, welcome the user by name and ask them if they are ready to play.
    """,
    output_key="user_name",
    tools=[get_user_name],
)



resumability_config = ResumabilityConfig(
    is_resumable=True
)

app = App(
    name='participant_hitl_agent',
    root_agent=participant_hitl_agent,
    resumability_config=resumability_config # <-- This is the critical line
)

and my error is

"""
/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/agents/invocation_context.py:302: UserWarning: [EXPERIMENTAL] BaseAgentState: This feature is experimental and may change or be removed in future versions without notice. It may introduce breaking changes at any time.
self.agent_states[event.author] = BaseAgentState()
2025-11-20 19:33:27,009 - ERROR - adk_web_server.py:1431 - Error in event_generator: the JSON object must be str, bytes or bytearray, not dict
Traceback (most recent call last):
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/cli/adk_web_server.py", line 1421, in event_generator
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/runners.py", line 454, in run_async
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/runners.py", line 442, in _run_with_trace
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/runners.py", line 654, in _exec_with_plugin
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/runners.py", line 431, in execute
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/agents/base_agent.py", line 291, in run_async
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/agents/llm_agent.py", line 460, in _run_async_impl
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 346, in run_async
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 365, in _run_one_step_async
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 455, in _preprocess_async
async for event in agen:
File "/Users/ashwjosh/miniconda3/lib/python3.12/site-packages/google/adk/flows/llm_flows/request_confirmation.py", line 84, in run_async
json.loads(function_response.response['response'])
File "/Users/ashwjosh/miniconda3/lib/python3.12/json/init.py", line 339, in loads
raise TypeError(f'the JSON object must be str, bytes or bytearray, '

"""

I am following the example at

Workflow -
I do get the confirmation screen in which I add the response like

{
"confirmed": true,
"payload": { "user_name": "ashwin" }
}

after which I get the error pasted above. I am trying ot make a trivia game with multiagent workflows. Any help would be appreciated.

I am using latest ADK

(base) ashwjosh@HK4T3VJL9J agents % pip freeze | grep google-adk
google-adk==1.19.0