Updating participant attributes via PATCH /api/v2/conversations/voice fails with 400

I’ve been trying to update custom participant attributes mid-call using the Genesys Cloud Conversations API. The goal is to flag a call as ‘compliance_checked’ once the IVR validates the user’s identity. I’m using the Python SDK for this, specifically the put_conversation_participant method, but I keep hitting a wall.

Here’s the snippet I’m working with:

from genesyscloud.conversations import ConversationsApi
from genesyscloud.models import ConversationParticipantUpdate

# ... auth setup omitted ...

body = ConversationParticipantUpdate(
 attributes={
 "compliance_checked": "true",
 "risk_level": "low"
 }
)

try:
 api_instance = ConversationsApi(api_client)
 api_instance.put_conversation_participant(
 conversation_id=conversation_id,
 participant_id=participant_id,
 body=body
 )
 print("Attributes updated successfully")
except Exception as e:
 print(f"Failed: {e}")

The response I get back is a 400 Bad Request with the message Invalid request body. I’ve verified the conversation_id and participant_id are correct by logging them right before the call. The JSON payload looks valid when I print body before sending it.

I’ve checked the API docs for /api/v2/conversations/{conversationId}/participants/{participantId} and it seems like a PUT request should work for updates. But wait, the docs also mention that some fields are read-only. Are attributes writable mid-conversation? I tried sending just the attributes object, but it didn’t help.

Also, I noticed that if I try to update the routing object instead, I get a different error about missing required fields. Is there a specific structure I’m missing for the attributes update? I’ve seen examples online using PATCH, but the SDK method is named put_conversation_participant. Could that be the issue?

I’m stuck. Any idea what’s causing the 400? I’ve tried wrapping the attributes in different objects, but nothing works. The error message isn’t very helpful either.

Are you sending the put payload or actually trying to patch? You mentioned PATCH in the title but used put_conversation_participant in the code. That’s likely your first issue. The Python SDK’s put method replaces the entire participant object. If you drop required fields like id or routing, the server throws a 400.

For mid-call attribute updates, you want the PATCH endpoint. It merges changes without requiring the full object. Here’s the working pattern using the SDK:

from genesyscloud.conversations import ConversationsApi
from genesyscloud.conversations.models import ConversationParticipantPatch

# Initialize API client
conversations_api = ConversationsApi(platform_client)

# Build the patch object
patch_body = ConversationParticipantPatch(
 custom_attributes={
 "compliance_checked": True
 }
)

# Execute the patch
try:
 conversations_api.patch_conversation_participant(
 conversation_id=conv_id,
 participant_id=part_id,
 body=patch_body
 )
except Exception as e:
 print(f"Patch failed: {e}")

The ConversationParticipantPatch model is strict. Only include fields you actually want to change. Sending extra keys can cause validation errors. Also, check your OAuth scope. You need conversation:modify and conversation:view. Missing modify will give you a 403, not a 400, but it’s easy to mix up if you’re debugging headers.

Watch out for async timing. If you patch right after the call connects, the participant ID might not be fully resolved in the backend yet. Add a small delay or check the conversation state first. The API isn’t always instant with state replication.

I’ve seen this break when people try to send nested JSON in custom attributes. Keep it flat. Key-value pairs only. No arrays, no objects inside objects. The backend parser for participant attributes is basic.