Need To Adapt Add On From 4.1.2 To 4.2.4

Hello im implementing payment gateway add on for cs cart, the post to payment dateway server is OK, but the confirmation from the payment gateway to cs cart was left me confuse

Here's the respond / log :

[FetchError] POSTHeader: HTTP/1.0 301 Moved Permanently
Date: Tue, 04 Aug 2015 02:45:58 GMT
Server: Apache/2
X-Powered-By: PHP/5.5.16
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Last-Modified: Tue, 04 Aug 2015 02:45:58 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: sid_customer_a5fa6=078407c68fc7bc3055d53824fab8059a_1_C; expires=Tue, 18-Aug-2015 02:45:58 GMT; Max-Age=1209600; path=/;; HttpOnly
Vary: User-Agent
Content-Length: 0
Connection: close
Content-Type: text/html; charset=utf-8

I have try all combination and it didnt work,because im no expert of cs cart, can someone help me? at least explain to me what really happen?

Really thank you

Can you specify return URL anywhere (in your code or merchant dashboard)? What value do you have there?