I wrote a quick tool to check if this function is available to the system with your server configuration.
ctype.php
<?php
if(function_exists("ctype_alnum")) {
echo("The PHP Function \"ctype_alnum\" was found on this system.");
} else {
echo("The PHP Function \"ctype_alnum\" was <b>NOT</b> found on this system.");
}
echo("\n<br><br>\n");
echo("The \"<a href=\"https://www.php.net/manual/en/function.ctype-alnum.php\" target=\"_blank\">ctype_alnum</a>\" function should be installed by default on PHP 4.0.4+, PHP5, PHP7, PHP8. If this function has not been located on your machine please install it or choose a different available PHP version.");
?>The ctype_alnum function is provided in all builds of PHP after PHP4.0.4; if it is missing on your system it'd likely be disabled through the php.ini on the server.
We've tested PHP7.4 here on UBBCentral on UBB.threads v7.5.5 and are able to submit mail messages (email thread is the general test) with no issues.
