Outbound predictive campaigns on our AP-1 BYOC trunk are stalling with HTTP 503 errors once concurrent calls exceed 300. The trunk remains registered, and latency to the carrier gateway is nominal. Architect flow logs indicate the dial-out step fails immediately after SIP INVITE. Has anyone seen this specific 503 behavior linked to carrier-side concurrency limits rather than Genesys platform throttling? Need insights on distinguishing platform vs. carrier rejection.