POST /api/v2/conversations/calls failing with 400 Bad Request on agentId

NICE CXone API & Integrations
1

Trying to initiate an outbound call for our WFM adherence testing. The endpoint POST /api/v2/conversations/calls keeps rejecting the payload. Here’s the JSON I’m sending:

{
 "providerId": "",
 "agentId": "550e8400-e29b-41d4-a716-446655440000",
 "to": "+15551234567",
 "from": "+15559876543"
}

Getting a 400 Bad Request. The error says the agentId is invalid, but the UUID exists in the directory. Am I missing a specific permission or format requirement?