As for me, the most crucial thing in a payment gateway is security! Everything else is secondary! The problem is that it is challenging to determine their vulnerabilities at a glance. My team and I tested some payment gateways last year and realized they all had some problems.
Yes, I see it without testing! You go to the news feed and find reports of hacks almost every day. This is especially true for crypto gateways! At first glance, the blockchain should provide good protection, but everything turns out somehow differently in practice.
Yes, I attribute this to the fact that the technology is only developing, and, unfortunately, well-thought-out protection systems have not yet been created. Although I greatly respect the blockchain, I must say that there is still work to be done here!