POST /api/v2/flows/executions 400 Bad Request

Trying to trigger an Architect flow from our Node.js service. Getting a 400 error with ‘Invalid request body’.

Here is the payload:

POST /api/v2/flows/executions
{
 "flowId": "123456",
 "inputs": { "userId": "user-001" }
}

The flow works manually. Is there a specific format for the inputs object when calling this endpoint?