Participant attributes vanishing during live voice call PATCH

genesyscloud-node-sdk handles the initial connection fine, but the custom attributes just vanish once the voice session moves past the queue. We’re hitting /api/v2/conversations/voice/${convId}/participants/${agentId} with a PATCH and sending this payload:

{
 "customAttributes": {
 "ext_ref": "tokyo-884",
 "priority_flag": "true"
 }
}

The endpoint returns 200 OK yet it’s reading null for {{conversation.participant.customAttributes.ext_ref}} a few seconds later, so I’m guessing we’re missing the X-Genesys-Application header or need to enable the writeCustomAttributes toggle on the integration settings first