GTpay is payment gateway for Nigerian People that maintained by Interswitch. As we know Nigeria is very unique country for money transfer or payment. Due to legal issue, it's not easy to send money from Nigeria. Moneygram or Western Union is operating in Nigeria but they just serve local transfer. They don't serve overseas transfer from Nigeria. Paypal and Moneybookers is not serving transfer money from Nigeria.
Company or people who have business in Nigeria use GTPay to receive payment from Nigerian Customer. By using GTPay, Nigerian customer can pay using Nigerian Debit card.we can use OSCommerce, Virtuemart, Magento, or other estore system. but they all doesn't have original module to handle payment through GTPay.
I see Softdb.eu provide GTPay module for Nagento in http://softdb.eu/gtpay-gtbank-magento-payment-gateway-p-34.html. but after paying that module, it's not working well in Magento and doesn't meet with Interswitch requirement. so we have to change the module and make customization. Softdb.eu is not good on after sales support. They said that we will get 30 days of free support. but when I contacting them using email, Skype, ICQ, etc, there's no response. So I make my own customization, and the lucky is I am successful to make it working.
I implemented this module for http://www.yesidefashionstore.com and http://www.usashoppinglinkstore.com. I also make my own module to implement GTPay-Interswitch gateway for OSCommerce system and it's implemented on http://bubbles4magodo.biz and http://telled.co.uk/
Please email me if you need my service to do GTPay installation on your estore system.