We'd need some more info on your systems and how they are configured to be able to provide any type of detailed guidance.
Where are the system registered? SIP or H.323? What is the call type, and how are the endpoints configured for CallSetup (Gatekeeper or Direct)? How are you connecting with Zoom - but dialling out, or having Zoom dial in? The more information you can provide us, the better we will be able to target any troubleshooting.
Wayne
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