Looking for advice on a stubborn SIP trunk registration issue that popped up during our migration from Zendesk Talk to Genesys Cloud. We are moving a mid-sized support team from France, and while the digital channels migrated smoothly, the telephony piece is hitting a wall.
In Zendesk, setting up the PSTN was largely handled by their integrated partners, so we didn’t deal much with raw SIP credentials. Now, configuring the SIP trunk in Genesys Cloud Admin > Telephony > SIP Trunks feels like stepping into a deep technical rabbit hole. We have generated the SIP credentials and entered them into our carrier’s portal, but the trunk status remains Offline.
The carrier logs show that Genesys Cloud is sending the REGISTER request, but it’s being rejected. Here is the exact error we are seeing in the Genesys Cloud SIP trunk diagnostic logs:
SIP/2.0 403 Forbidden
From: <sip:[email protected]>;tag=abc123
To: <sip:[email protected]>;tag=xyz789
Call-ID: [email protected]
CSeq: 1 REGISTER
Content-Length: 0
We have double-checked the username, password, and domain in both the Genesys Cloud SIP trunk configuration and the carrier’s side. The IP addresses in the allowed list also match our public IP. Since this is my first time dealing with SIP trunking at this level, I am wondering if there is a specific header mismatch or a timing issue with the REGISTER request that Genesys Cloud sends compared to what Zendesk’s underlying infrastructure might have used.
Is there a way to force a re-registration or view the raw SIP message payload being sent by Genesys Cloud? In Zendesk, we had less visibility into the SIP stack, so this level of debugging is new territory for me. Any pointers on what typically causes a 403 Forbidden in this context would be greatly appreciated. We are aiming to go live next week, so getting the phone lines up is priority number one.
Check your SIP authentication credentials and ensure the username matches the exact format Genesys Cloud expects, which is often domain/user or just user depending on the edge configuration. The 403 Forbidden error usually indicates a credential mismatch or an IP restriction issue rather than a protocol error. When migrating from Zendesk, the SIP URI scheme might differ, so verify the “User” field in the Genesys Cloud SIP trunk settings matches the username provided by your ITSP. If using a BYOC setup, confirm that the public IP of the outbound proxy is whitelisted in the Genesys Cloud SIP Trunk settings under “Allowed IPs”. Also, review the WebSocket connection limits if you are testing this via a load tool like JMeter; rapid re-registration attempts can trigger rate limiting that manifests as authentication failures. Here is a basic JMeter configuration snippet to test the registration stability without overwhelming the edge:
<HTTPSamplerProxy guiclass="HttpTestSampleGui" testclass="HTTPSamplerProxy" testname="SIP Reg Test">
<elementProp name="HTTPsampler.Arguments" elementType="Arguments">
<collectionProp name="Arguments.arguments"/>
</elementProp>
<stringProp name="HTTPSampler.domain">sip.genesys.cloud</stringProp>
<stringProp name="HTTPSampler.port">5060</stringProp>
<stringProp name="HTTPSampler.protocol">sip</stringProp>
<stringProp name="HTTPSampler.path">/register</stringProp>
</HTTPSamplerProxy>
Ensure the “Concurrent Threads” in JMeter is set low (e.g., 1-5) during the initial verification phase. High concurrent registration attempts can cause the edge to temporarily block the source IP, resulting in 403s. If the credentials are correct, check the Genesys Cloud system logs for specific SIP error codes related to “Authentication Failed” or “IP Not Authorized”. Sometimes, the ITSP requires a specific SIP domain in the “From” header, which Genesys Cloud might not be sending by default. Adjust the SIP trunk settings to include the correct domain suffix if required by the provider. This approach helps isolate whether the issue is credential-based or network-based.