Fatal error: Uncaught LearnositySdk\Exceptions\ValidationException: The `secret` argument must be a valid string in /var/www/html/vendor/learnosity/learnosity-sdk-php/src/LearnositySdk/Request/Init.php:481 Stack trace: #0 /var/www/html/vendor/learnosity/learnosity-sdk-php/src/LearnositySdk/Request/Init.php(141): LearnositySdk\Request\Init->validate() #1 /var/www/html/test-latex.php(38): LearnositySdk\Request\Init->__construct() #2 {main} thrown in /var/www/html/vendor/learnosity/learnosity-sdk-php/src/LearnositySdk/Request/Init.php on line 481