sign
Enrolls the member in ActivePerks with a payment card.
On success the returned ActivePerksEnrollment.isEnrolled is true; its enrollmentState is null right after signup (the server sends no status on that branch).
Return
The post-signup ActivePerksEnrollment.
Parameters
details
Card and billing details; see ActivePerksSignUpDetails for the exact formats the server enforces.
Throws
if enrollment fails (declined card, existing account, validation) - the server's error detail rides on the thrown AFException.