Fatal error: Uncaught Error: Call to undefined function Facebook\PseudoRandomString\mb_substr() in /home/vacunita/public_html/tfcol/web/dev/test/facebook-sdk/src/Facebook/PseudoRandomString/PseudoRandomStringGeneratorTrait.php:56 Stack trace: #0 /home/vacunita/public_html/tfcol/web/dev/test/facebook-sdk/src/Facebook/PseudoRandomString/OpenSslPseudoRandomStringGenerator.php(65): Facebook\PseudoRandomString\OpenSslPseudoRandomStringGenerator->binToHex() #1 /home/vacunita/public_html/tfcol/web/dev/test/facebook-sdk/src/Facebook/Helpers/FacebookRedirectLoginHelper.php(153): Facebook\PseudoRandomString\OpenSslPseudoRandomStringGenerator->getPseudoRandomString() #2 /home/vacunita/public_html/tfcol/web/dev/test/facebook-sdk/src/Facebook/Helpers/FacebookRedirectLoginHelper.php(170): Facebook\Helpers\FacebookRedirectLoginHelper->makeUrl() #3 /home/vacunita/public_html/tfcol/web/application/templates/tfcol/assets/html/login.phtml(22): Facebook\Helpers\FacebookRedirectLoginHelper->getLoginUrl() #4 /home/vacunita/public_html/tfcol/web/application/classes/class.template.php(154): include_once('/home/vacunita/...') #5 /home/vacunita/public_html/tfcol/web/application/classes/class.template.php(180): template->loadHTML() #6 /home/vacunita/public_html/tfcol/web/application/classes/class.template.php(22): template->loadLayout() #7 /home/vacunita/public_html/tfcol/web/application/classes/class.application.php(73): template->__construct() #8 /home/vacunita/public_html/tfcol/web/application/init.php(29): application->__construct() #9 /home/vacunita/public_html/tfcol/web/index.php(12): require_once('/home/vacunita/...') #10 {main} thrown in /home/vacunita/public_html/tfcol/web/dev/test/facebook-sdk/src/Facebook/PseudoRandomString/PseudoRandomStringGeneratorTrait.php on line 56