pmpro_checkout_start_date

This hook pmpro_checkout_start_date allows you to change the start date of a membership before checkout. 

apply_filters( "pmpro_checkout_start_date", $startdate, int $user_id, object $pmpro_level );

pmpro_subscription_payment_completed

For PayPal and TwoCheckout only. Execute custom code before saving a successful order.

do_action("pmpro_subscription_payment_completed", $morder);

pmpro_subscription_payment_failed

Execute custom code when a subscription payment fails. Passes the last successful MemberOrder object.

do_action("pmpro_subscription_payment_failed", MemberOrder $old_order);