manual payments automatic update

Maybe you have answered this before, but I really could not find the information.

I would like to give to the manual payment a link that updates the payment without having to be sitting checking each user.

I explain myself, I currently have some activation buttons for free membership, so after acquiring the free membership, people are redirected to a page that asks them to ” Activate Membership “. and this is activated automatically without my intervention.

I use this:
$m_app = MS_Controller_Api::instance();
$membership = $m_app->get_membership( $membership_id );
$member = MS_Factory::load( ‘MS_Model_Member’, $user_id );
if ( $member ) {
//admin :: free 🙂 but you can replace it with the appropriate payment gateway
$subscription = $member->add_membership( $membership->id, ‘admin’ );
// Activate free memberships instantly. Not sure if this will be handy.
if ( $membership->is_free() ) {
$subscription->add_payment( 0, MS_Gateway_Free::ID, ‘free’ );
}
}

I would like to do the same with the paid memberships. I do not use Paypal or the other systems that have the pluging, since in my country I could not charge that money. I use PAyU, PayU returns after the effective payment to a link that I assign. For this reason, I would like to be able to do the same thing that I do with the free membership.