BYOC Trunk 503 during JMeter burst on US1

Context:

Testing Bring Your Own Carrier (BYOC) trunk capacity on Genesys Cloud US1. JMeter sends 40 concurrent SIP INVITE requests to the Genesys SIP trunk endpoint. The flow uses standard Architect routing with a simple IVR. Response is 503 Service Unavailable after 10 seconds. JMeter version 5.6.2. Thread group uses 40 threads with no ramp-up. This blocks our capacity planning for peak call volumes.

Question:

Is it possible to configure the BYOC trunk to handle this burst without returning 503? The error suggests the Genesys SIP interface is overwhelmed. We need to understand the concurrent call limit for BYOC trunks in US1. Our current test hits 40 concurrent threads. The 503 response prevents us from validating our routing logic under load. Payload below:

INVITE sip:gen-sip-us-east-1.genesys.cloud SIP/2.0
Via: SIP/2.0/TCP 192.168.1.100:5060;branch=z9hG4bK12345
Max-Forwards: 70
To: <sip:[email protected]>
From: <sip:test@192.168.1.100>;tag=12345
Call-ID: test-12345
CSeq: 1 INVITE
Contact: <sip:test@192.168.1.100:5060>
Content-Type: application/sdp
Content-Length: 200

Any configuration changes to increase capacity?