add hooks

WooCommerce comes with a large set of actions and filteres that you can use to do custom actions.

When it comes to purchases, no matter what payment gateway is used, the woocommerce_payment_complete action will fire as an example.

You could use this hook to award points i.e.:

add_action( 'woocommerce_payment_complete', 'add_points_for_woo_purchase' );
function add_points_for_woo_purchase( $order_id ) {
	if ( ! function_exists( 'mycred_add' ) ) return;
	mycred_add( 'purchase_reward', get_current_user_id(), 100, 'Points for store purchase' );
}