includes/class-freemius.php
public function track_event_once( $name, $properties = array(), $process_at = false ) {
            return $this->track_event( $name, $properties, $process_at, true );
        }
public function track_event_once( $name, $properties = array(), $process_at = false ) {
            return $this->track_event( $name, $properties, $process_at, true );
        }
public function track_event_once ( $ name , $ properties = array ( ) , $ process_at = false ) { return $ this -> track_event ( $ name , $ properties , $ process_at , true ) ; }
Track install's custom event only once, but it still triggers the API call.

IMPORTANT:
Custom event tracking is currently only supported for specific clients.
If you are not one of them, please don't use this method. If you will,
the API will simply ignore your request based on the plugin ID.

Need custom tracking for your plugin or theme?
If you are interested in custom event tracking please contact yo@freemius.com
for further details.

@author Vova Feldman (@svovaf)
@since  1.2.1

@param string $name       Event name.
@param array  $properties Associative key/value array with primitive values only
@param bool   $process_at A valid future date-time in the following format Y-m-d H:i:s.

@return object|false Event data or FALSE on failure.

@throws \Freemius_InvalidArgumentException

@user   Freemius::track_event()
Track install s custom event only once but it still triggers the API call .