Exchange UM and Skype for Business VoiceMail intergration

I have an SFB2015 setup with Exchange 2013(2 x CAS/Mailbox servers and one mailbox server.)  I have enabled Voicemail and it says it has worked, but I cannot connect to voicemail or get the test to work.
On the SFB box I am getting








PS C:\Users\administrator.APTC> Test-CsExUMConnectivity -TargetFqdn "sfb15.domain.local" -UserSipAddress "sip:user.name@domain.com" -UserCredential $cre
dential


Target Fqdn   : sfb15.domain.local
Result        : Failure
Latency       : 00:00:00.1552189
Error Message : 480, Temporarily Unavailable


Diagnosis     : ErrorCode=1038,Source=SFB15.domain,Reason=Failed to
                connect to a peer
                server,appname=ExumRouting,dialplan=CSSUM.domain.local
                Microsoft.Rtc.Signaling.DiagnosticHeader



On the CAS box


The Microsoft Exchange Unified Messaging Call Router service failed to process a user notification event with the following parameters:
From: "sip:A410AA79-D874-4e56-9B46-709BDD0EB850",
To: "sip:EX13-CAS1.domain.local;opaque=app:rtcevent;transport=tls",
Response code: "500"
Diagnostic header: "ms-diagnostics-public:15604;source="EX13-CAS1.domain.local";reason="Transient error.""
User: "EUM:sip:user.name@domain.com;phone-context=CSSUM.domain.local"
Backend: "EX13-HTS1.domain.local".


I have a similar setup on my own SFB/EX13 box and it works perfectly.  I have tried to see what I have done wrong but keep hitting the same wall.

I can't tell if this is purely a certificate issue or some other issue I am missing.