what good resource to learn to build large scale payment Service or apps

i'm Web Laravel Developer with almost 3yr experience in SWE in general. mostly CRUD systems

now I want to learn how I can build Large Scele Fintech apps and payment services like Stripe – Paypal – Payoneer … etc

I know how complex these systems are and it requires an army of programmers .. but I want to learn how to build Solid MVP at least

any Good resources MOOCs or Books