Please show me the regulation that tells me whether to use big decimals or integers in my internal monetary amount representation. Regulations usually care about outcomes (sometimes high, sometimes low level); they often don't tell you how to technically achieve them.

And if your lawyers and compliance people are actually telling you that you can absolutely not do any financial processing yourself, that the only possible way to be compliant is to license <incumbent product xyz> (unfortunately only available in COBOL) etc., you might not actually be working in a fintech, or at least not in the kind this guide seems to be targeted to.

Frankly, this kind of attitude is exactly why banking and payments is as fossilized as it is in some countries, and why fintech is eating their lunch in many cases. There has to be a balance between trying new things and doing what everybody else is already doing.