If you want to build a payment gateway from scratch or license one of online gateway solutions to provide gateway services under your own brand, you need to understand the key aspects of the process. Building or licensing your own payment gateway involves two conceptual aspects: business and technical. First, in order to be able to provide online payment gateway services, beside the gateway solution itself, you need an acquiring bank partnership. Partnership with a merchant acquirer (sometimes called credit card acquirer) concerns the business aspect of payment gateway services provision. It is your point of entry into the banking system. And keep in mind that an acquiring bank is not an ordinary commercial bank where you have a checking account. It is a special type of bank that provides merchant services (issues merchant accounts and underwrites you as a merchant, PayFac, or gateway provider), and assumes the liability for your operations (including chargeback and fraud risks). The technical aspect is installation of payment gateway software in the PCI compliant environment. This will allow you to process transactions for your customers that accept credit cards, debit cards, and, accept payments online in general. For this purpose you need to get the respective specifications from the acquirer. So, as you can see, business aspect, i.e. acquiring bank partnership goes first.
Read more about starting a payment gateway solution in our respective article on Paylosophy.