I am currently using Zencart 1.5.4 and I have decided to do a new install of 1.5.7c in a different folder and do some major changes/upgrades. I have upgraded the PHP to 7.4.
I am getting the 500 Error after clicking on the new install link and the following is in the log (used MyURLFolder in place of address).

PHP Fatal error: Uncaught Error: Call to undefined function ctype_digit() in /MyURLFolder/zc_install/includes/vendors/yaml/lib/class.sfYamlInline.php:402
Stack trace:
#0 /MyURLFolder/zc_install/includes/vendors/yaml/lib/class.sfYamlInline.php(202): sfYamlInline::evaluateScalar('systemChecks')
#1 /MyURLFolder/zc_install/includes/vendors/yaml/lib/class.sfYamlParser.php(125): sfYamlInline:arseScalar('systemChecks')
#2 /MyURLFolder/zc_install/includes/vendors/yaml/lib/class.sfYaml.php(97): sfYamlParser->parse('#\n# @copyright ...')
#3 /MyURLFolder/zc_install/includes/classes/class.systemChecker.php(17): sfYaml::load('#\n# @copyright ...')
#4 /MyURLFolder/zc_install/includes/modules/pages/index/header_php.php(28): systemChecker->__construct('admin')
#5 /MyURLFolder/zc_install/index.php(40): require('/hermes/walnacw...')
#6 {main}
thrown in /MyURLFolder/zc_install/includes/vendors/yaml/lib/class.sfYamlInline.php on line 402

Can you tell me what I am doing wrong or need to change? Or direct me to the message thread that covers this issue? Thanks.