WordPress caught an error with one of your plugins, Clickbank Storefronts.

Error Details
=============
An error of type E_ERROR was caused in line 788 of the file /hermes/bosnacweb01/bosnacweb01/bosnacweb01at/b1876/ipg.dkhoddercom/testing/wp-content/plugins/clickbank-storefront/admin.inc.php. Error message: Uncaught Error: Call to undefined function ctype_digit() in /hermes/bosnacweb01/bosnacweb01/bosnacweb01at/b1876/ipg.dkhoddercom/testing/wp-content/plugins/clickbank-storefront/admin.inc.php:788
Stack trace:
#0 /hermes/bosnacweb01/bosnacweb01/bosnacweb01at/b1876/ipg.dkhoddercom/testing/wp-includes/class-wp-hook.php(307): cs_option('')
#1 /hermes/bosnacweb01/bosnacweb01/bosnacweb01at/b1876/ipg.dkhoddercom/testing/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters('', Array)
#2 /hermes/bosnacweb01/bosnacweb01/bosnacweb01at/b1876/ipg.dkhoddercom/testing/wp-includes/plugin.php(476): WP_Hook->do_action(Array)
#3 /hermes/bosnacweb01/bosnacweb01/bosnacweb01at/b1876/ipg.dkhoddercom/testing/wp-admin/admin.php(259): do_action('settings_page_c...')
#4 /hermes/bosnacweb01/bosnacweb01/bosnacweb01at/b1876/ipg.dkhoddercom/testing/wp-admin/options-general.php(10): require_once('/hermes/bosnacw...')
#5 {main}
  thrown

I get this error when I try to update the setting to the Storefront Plugin or the Niche Storefront plugin. PBProads lifetime Pro Member.

Installation: WordPress 6.1.1 also installed to WordPress 6.0.3 with same results.