Getting error “Call to undefined function catchException()” in php chunk of code

I am making a class in php whose definition is given below.

<?php
    // A PHP class to log every exception on bugsnag account.
    // All classes that make 3rd party request must extend this class

    // importing all the dependencies
    require_once realpath('bugsnag.phar');
    require_once realpath('guzzle.phar');
    require_once realpath('vendor/autoload.php');

    class BugSnagLogger {
        
        private $bugsnag;
        private $bugSnagAPIKey;

        // Initializing the BugSnag Instance in the constructor itself.
        public function __construct($bugSnagAPIKey) {
            $this->bugSnagAPIKey = $bugSnagAPIKey;
            $this->$bugsnag = BugsnagClient::make($this->bugSnagAPIKey);
            BugsnagHandler::register($this->$bugsnag);
        }

        // Method to catchExceptions.
        public function catchException(Exception $exception) {
            $this->bugsnag->notifyException($exception);
        }
    }

    $logger = new BugSnagLogger('a7ce9f54025c3873c34775e8a7001e6e');
    $logger.catchException(new Exception('Custom Exception by Sparsh.'));
?>

On Executing the above code I am getting the error Call to undefined function catchException(). I don’t know what I am doing wrong in this case, can someone please help me with this ?.