Incoming call fail on 5312 phone with 3rd party server

[Den Li]

Dear All,

I connected Mitel 5312 phone (SIP mode) with 3rd party sip provider but only outgoing call is working. All incoming call is fail.
I used another Yealink T21 phone connected to same sip provider from same office network. The Yealink phone is no problem
Anything I missed on Mitel phone?! Please help.

Thanks,

Den