[SOLVED] 2Checkout INS problem with WHMCS - Call back notification not Working

We had an issue with 2Checkout notifications with WHMCS, really tried to fix it but in vain. When we contacted WHMCS, they responded as below:

Hello,

Thank you for coming back to me here.

This is most strange.

I have checked and confirm the callback URL is accessing and returns a 200 response:

[root@alex ~]# curl -X HEAD -i https://register.navicosoft.com/modules/gateways/                                                                                                                                                             callback/tco.php
HTTP/1.1 200 OK
Date: Tue, 27 Feb 2018 12:58:31 GMT
Server: Apache
X-Powered-By: PHP/5.6.33
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: WHMCSMMsXNw2HK4x5=eaun73461hucpn27cu5soec3f7; path=/; secure; HttpOn                                                                                                                                                             ly
Access-Control-Allow-Origin: *
Content-Type: text/html; charset=utf-8

The data being sent looks good to me and so do the configuration settings inside your 2checkout account.

Could you please try one, or if possible, both of the following:

1) Remove the secret word from both WHMCS and 2checkout, then test again.
2) Test in demo mode - In order to use demo mode, the "Demo Setting" in your 2CheckOut account should be set to "Parameter" under Account > Site Management. Demo mode can then be enabled by ticking the checkbox in WHMCS under Setup > Payments > Payment Gateways.

Please let me know the results of this.

We did our level best in order to fix this issue but it never worked. Then we contacted 2CO team and they responded with the followings:

Thank you for reaching out to us and apologies for the late reply.

When checking the INS logs on our server we can see the following:

==
Fail Reason: Internal System Error
Exception: OpenSSL::SSL::SSLError: SSL_connect returned=1 errno=0 state=SSLv2/v3 read server hello A: sslv3 alert handshake failure
==

Please note that, in order to avoid further INS failures, we recommend disabling SSL v3 as it is not supported by our INS.
We recommend you to also check your internal logs and see if there any error messages received.

At this moment, a platform upgrade is under developement and further information will be provided in the near future.


Then after searching & surfing on the internet, the issue was found to be with our apache configuration:

The following solution worked for us:

Proposed Fix which was final solution to get it solved
(after investigating several sources)
========

SSLProtocol All -SSLv2 -SSLv3
SSLCipherSuite should be: ALL:!ADH:+HIGH:+MEDIUM:-LOW:-SSLv2:-EXP


This will work with Apache and also LiteSpeed, if you have this installed on your server.

Update: Indications are if running Litespeed, needs latest applied, 4.2.17 or newer.

Tests
Test your web server for SSLv2
https://www.ssllabs.com/ssltest/index.html

What you are looking for is:
TLS 1.2 Yes
TLS 1.1 Yes
TLS 1.0 Yes
SSL 3 No
SSL 2 No

Good luck!