good question

i list for you the main problems with entering this space:

criminal liability for mistakes (AML rules), you have to manage fraud, the banks which are your custody providers will constantly try and shut you down, clients expect your service on day one to be equal to mastercard, your margins are almost nothing, it is one of the most competitive industries in the world, you need to go through central bank regulations/SEC equivalent every time you enter a new market, governments in countries like Vietnam or Bangladesh or China are actively hostile to your business model, and it is HYPER competitive. anything you do well, stripe/airwallex/etc will clone immediately

Airwallex is one of the most powerful stripe competitors and the CEO is a psychopath that seems like a tv parody of a silicon valley CEO. he has to be though because so many governments, banks, competitors etc are trying to crush him constantly.

note that stripe differentiates itself heavily on checkout technology, basically making the experience of paying for things easier for the consumer.