Cannot use service desk plus from Internet

Cannot use service desk plus from Internet

We are facing a probem to access the service desk plus using https access from Internet, the service deskplus is running in our internal network end is natter to a public IP. We have succesfully installed a valid ssl certificate using letsencrypt. From our firewall logs it is aparent that the NAT to the internal system is working fine and requests Public network are reaching the system, however, we are getting no response from service desk system to these request and the home login page is not getting displayed. Further we have noticed that the incoming requests from public network were using ssl v3 negotiations and were getting dropped, we have opened sslv3 too in our forewall but the same problem persists. We are using service desk plus 11.1
Is there any  port  number  for open this  service desk plus OR  any other configuration its need to be done?  Please suggest. 

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