Set Participant Data action not persisting custom variables in Kotlin SDK

Architect & Flows
1

Trying to push a custom variable loyaltyId through an IVR flow using the Set Participant Data action. The API call to set participant data returns 200 OK, but the variable never shows up in downstream actions. Here’s the payload:

{
 "data": {
 "loyaltyId": "12345"
 }
}

Is there a specific mapping required in the Architect config for external data actions, or am I missing a flag in the request?