I am trying to install the plugin and get the following error:

Fatal error: Uncaught Error: Call to undefined function
ctype_digit() in
/hermes/bosnacweb04/bosnacweb04ac/b2570/myd.fellwoshiplodge1175c/newbuild/wp-content/plugins/wpforo/wpf-includes/functions.php:1002
Stack trace: #0
/hermes/bosnacweb04/bosnacweb04ac/b2570/myd.fellwoshiplodge1175c/newbuild/wp-content/plugins/wpforo/wpf-includes/functions.php(2322):
wpforo_bigintval('') #1
/hermes/bosnacweb04/bosnacweb04ac/b2570/myd.fellwoshiplodge1175c/newbuild/wp-content/plugins/wpforo/wpf-includes/functions.php(1314):
wpforo_wp_url_to_postid('wp-admin/plugin...') #2
/hermes/bosnacweb04/bosnacweb04ac/b2570/myd.fellwoshiplodge1175c/newbuild/wp-content/plugins/wpforo/wpf-includes/functions-installation.php(844):


I would appreciate any help to resolve this issue.