Ok, so you plan to integrate payment gateway to your website. You paid REMITA and all they tell you is that it's MERCHANT DIY "MERCHANT DO IT YOURSELF". After you have paid for your integration with Remita, you'll receive a couple of documents and instruction, now you'll need to setup.
Don't get trapped in the hashing world, it could take a longer time if you try to do it yourself, give it to me to handle in 24 hours
1. I'll setup the integration for you on any object-oriented website that you have.
2. I will also test end-to-end to ensure smooth payment
3. I will also follow this process until you're moved to the production environment.