Stop Rejected Calls from Ringing Other Endpoints
A single extension can be registered on more than one endpoint at the same time. An endpoint is any device or app signed in to that extension, for example a desk phone, the Cloud Voice App on a computer, and the Cloud Voice App on a phone all using the same extension number.
By default, when an extension is registered on several endpoints and the user rejects an incoming call on one of them, the call keeps ringing every other endpoint until someone answers or the call times out. This procedure changes that behavior so that a rejection on any single device silences all of the user’s endpoints at once. Enable this when a user wants a “no” on one device to mean “no” everywhere.
Enable all-reject mode
Section titled “Enable all-reject mode”-
Sign in to the Cloud Voice management portal and go to Extension and Trunk > Extension, then open the extension you want to change for editing.
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Select the Features tab.
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Under the Call section, tick All Reject Mode for Endpoints.

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Click Save.
What happens next
Section titled “What happens next”Once this setting is on, a rejection on any of the user’s devices immediately stops the remaining endpoints from ringing. The call is then handled by the extension’s When Busy destination, which you configure at Extension and Trunk > Extension > Presence > Call Forwarding.