Just about any payment method other then handing cash to someone has a reversal risk.
So, even if they fund with a debit card 6 weeks later the funds can be pulled back. So, now you have to acquire the BTC and sit on it until you are sure the funds clear.
How are you going to handle the KYC? There are a ton of places that will do it for you for a fee. But now they have access to your site / API calls so you are at risk that way.
And so on.
-Dave
There are KYC services that do not make external calls. For example, they provide you with an SDK that you bundle with your iOS/Android app. This parses documents, does liveness check etc. You then save these docs and results on your server.
Regarding the reversal risk, I work in online payments and, for the most part, we avoid reversals by forcing all paying with a debit/credit card through 3d secure. This shifts liability to the card holder. Actually what I want to do is a bit different - its pay by bank account. Its becoming more common now here in Europe due to increase in open banking.