Question - why do you think payment processors even exist? Why don’t huge companies with tons of workforce just process payments themselves and save millions of $ on paying the processor fees?

The answer is all the legal trouble and complications. So many regulations, so many liabilities, so many issues with security that companies decide that it’s worth spending a percentage of their multimillion-dollar revenue to not have to deal with.

And you are trying to do all that by yourself. This project is impossible.