Bug: Can't get past TOTP login page anymore

OS: Debian 12 Server: nginx PHP: PHP 8.3 Wallos: 4.8.2 When logging in I enter user name and password. Then TOTP page comes up. After I enter my TOTP and proceed on `/totp.php` page I receive a HTTP 500 error. This is from the nginx log. ``` 2026/04/26 16:45:56 [error] 2662899#2662899: *895446 FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught Error: Call to undefined function OTPHP\mb_strtoupper() in /var/www/wallos/libs/OTPHP/ParameterTrait.php:160 Stack trace: #0 /var/www/wallos/libs/OTPHP/ParameterTrait.php(121): OTPHP\OTP::OTPHP\{closure}() #1 /var/www/wallos/libs/OTPHP/ParameterTrait.php(133): OTPHP\OTP->setParameter() #2 /var/www/wallos/libs/OTPHP/OTP.php(28): OTPHP\OTP->setSecret() #3 /var/www/wallos/libs/OTPHP/TOTP.php(21): OTPHP\OTP->__construct() #4 /var/www/wallos/libs/OTPHP/TOTP.php(56): OTPHP\TOTP->__construct() #5 /var/www/wallos/totp.php(73): OTPHP\TOTP::createFromSecret() #6 {main} thrown in /var/www/wallos/libs/OTPHP/ParameterTrait.php on line 160" while reading response header from upstream ```