Shift Trade API 403 on Chicago WFM Cluster

Why does this setting block shift trades for agents with valid self-service permissions? The PATCH /api/v2/wfm/scheduling/agents/{agentId}/shifts endpoint returns a 403 Forbidden error despite correct role assignments. Here is the payload causing the failure:

{
 "tradeId": "trade-123",
 "status": "ACCEPTED",
 "agentId": "agent-456"
}