Not getting inventory from client

I am facing below error on client machine.

ERROR *** AGENT => Failed to send Prolog <Couldn't connect to server>

I am using cent OS 7 for ocsserver and my client machine is with windows 10.

Check OCSInventory log client machine (Win 10)

==============================================================================
<C:\ProgramData\OCS Inventory NG\Agent\cacert.pem>
    COM SERVER => Sending HTTP Post request to URL <http://192.168.2.20/ocsinventory>
    WARNING *** COM SERVER => Failed to send HTTP Post request <Couldn't connect to server>
    COM SERVER => Cleaning cURL library
ERROR *** AGENT => Failed to send Prolog <Couldn't connect to server>
AGENT => Unloading communication provider
AGENT => Unloading plug-in(s)
AGENT => Execution duration: 00:00:00.