Cisco CUBE - SIP Provider Inbound Call issue

[Remon.BA]

Dears 
This is new deployment for integration between 

CUCM 11.5 - CUBE (2911) ----SIP Provider

Inbound and outbound calls fail , but lets focus first on inbound .

As appeared CUBE sending 180 Ringing messages to SIP Provider without any response , i have shared these logs with Provider but no valued  feedback from their side

Attached logs for inbound call test and sh run 
Attached : debug ccsip messages 

Regarding CUCM Settings 
On SIP Trunk : MTP Enabled
Early offer coded g711alaw
and below is SIP Profile settings 

[Vaijanath Sonvane]

Hi @Remon.BA,

From the logs, the SIP call flow appears to be progressing normally. You will only see  200 OK followed by an ACK once the call is answered by Phone registered on CUCM. 

• Is the phone on CUCM not ringing? 
• Are you not getting ringing tone on callers phone? 

[Nithin Eluvathingal]

Could you ensure the call lands on the phone? From the logs I expect the call to ring on the phone .

If the call rings and you answer it by picking up the desk phone, since we don't see a 200 OK, I assume that CUCM didn't recognize the call was answered, causing it not to send the 200 OK to the gateway and the ITSP.

Is there a firewall between the CUCM and the IP phone? If yes, make sure you disable SIP inspection.

Your gateway configuration needs a lot of fine-tuning as it deviates significantly from best practices