AfterPay needs a fixed set of fields in order to do a risk check. The fields per payment method can be found here.
However, not all merchants have all fields in their checkout. For example, date of birth or gender are not always standard.
Forcing a merchant to ask for this extra personal info in their shop by default for all orders, regardless of payment method does not help conversion.
So, enable the merchant to ask for this information only when needed, for example when choosing AfterPay as a payment method (or in an separate payment page).
If a merchant does have fields in place for gender, DOB etc. then do not make an end-user give that information again.