SIP 403 Forbidden on INVITE during JMeter load test in US1

SIP 403 Forbidden errors are appearing when JMeter 5.6 sends 200 concurrent INVITE requests to our US1 SIP trunk. The test setup uses valid credentials and correct DIDs. Single-thread tests pass without issue.

The error occurs specifically when concurrency exceeds 50 calls per second. Is there a hidden rate limit on INVITE messages for standard SIP trunks in Genesys Cloud? Need help identifying if this is a configuration error or a platform restriction.