Each AfterPay payment method requires personal- and address information (to do a risk check). Please make sure you ask for this information in your checkout. Add fields where needed. You can choose to only ask for certain info (like date of birth or gender) when choosing AfterPay.
If fields are already available for gender, DOB etc. then do not ask for that information again. (you can have them as optional for example, in that case check if there is a value. If not then ask for them when choosing AfterPay)
The required fields are listed in the API documentation.