This action is used to do action only after user paid 0 amount for paid finite OR paid Infinite type of plan using Paypal payment gateway.

Hook Type: Action
Source: core/classes/class.arm_gateways_paypal.php
add_action( 'arm_after_paypal_free_payment', 'your_function', 10, 5);
function your_function($plan, $payment_log_id = 0 , $arm_is_trial = 0, $coupon_code = '', $extraParam = array()) {
     //Do Your Action
    //$plan plan object
    //$payment_log_id Payment ID
    //$arm_is_trial Is this payment of trial period?
    //$coupon_code Coupon code 
    //$extraParam Array of extra parameters
Plan Object
ID of row of database table where payment history added.
Whether user paid for trial period or not?
Coupon Code used while payment.
Array of extra parameters like plan_amount, paid_amount, coupon_amount etc.