Architect Data Action failing with 400 Bad Request during migration

Just noticed that the Data Action step in my Architect flow returns a 400 error when trying to map the Zendesk ticket ID to the interaction context. The payload structure matches the Zendesk API docs but GC rejects it immediately. Here is the JSON I am sending:

{
 "ticketId": "{{trigger.ticketId}}",
 "status": "open"
}

Is there a specific schema validation I am missing for the Zendesk-to-GC mapping?