Set Participant Data not updating variables for downstream Data Actions

Architect & Flows
1

Trying to pass custom variables through an IVR flow using the Set Participant Data action. The action executes without error, but subsequent Data Actions see null values. Here’s the JSON payload:

{
 "participantData": {
 "trace_id": "otel-span-123"
 }
}

Is there a delay before these vars are available? Or do I need a specific context flag?