How can I set a registered client to never expire?
There is no setting to set a client never expires.
Instead, set long period.
For Example, set the Dial Plan rule as below.
----------------------------------------- [Matching Pattern] $request = ^REGISTER [Deploy Pattern] $action = register &net.registrar.adjust.expires = 31536000 -----------------------------------------
It sets 31536000 seconds for the expire period, which is equal to 1 year.