Allow caller from pstn can call direct extension on another pbx

My system is server1 with ext (7xxx) trunk to server 2 with ext (8xxx)
Now i want caller from pstn of server 1 can direct dial extension on server 2.
The caller to server 1 can call direct dial extension on it.
Thanks for all.
Note : pstn -> ivr (server1) ->7xxx (yes)
->8xxx (no - invalid extension )

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I found,thanks all.