Fatal Error after clean install of 2.1.0

Did a clean Install of Zen Cart 2.1.0 (PHP Level ea-php83), in its own subdomain (production is in another subdomain running PHP Level ea-php72). Installation completed with just a warning "PHP GZip extension not detected. ... Your hosting company can take care of this for you.". Hosting company response was "PHP Gzip should be enabled at the moment, I have as well tested through PHP script and seems to be working as intended." So I continued.

Installation successfully completed; however, I get a 500 Fatal Error attempting to access both the storefront and admin. I admit I'm in over in over my head but would really like to see this through.

Most profuse thanks in advance for any assistance you can provide.

Error log:

[22-Jan-2026 17:08:29 UTC] PHP Fatal error: Uncaught Error: Call to undefined function Symfony\Polyfill\Mbstring\iconv_substr() in /home/soldiers/public_html/dev-2025/laravel/vendor/symfony/polyfill-mbstring/Mbstring.php:667
Stack trace:
#0 /home/soldiers/public_html/dev-2025/laravel/vendor/symfony/polyfill-mbstring/bootstrap80.php(72): Symfony\Polyfill\Mbstring\Mbstring::mb_substr('configuration', 0, 1, 'UTF-8')
#1 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/support/Str.php(1135): mb_substr('configuration', 0, 1, 'UTF-8')
#2 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/support/Str.php(1205): Illuminate\Support\Str::substr('configuration', 0, 1)
#3 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/support/Str.php(1119): Illuminate\Support\Str::ucfirst('configuration')
#4 [internal function]: Illuminate\Support\Str::Illuminate\Support{closure}('configuration')
#5 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/support/Str.php(1119): array_map(Object(Closure), Array)
#6 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Concerns/HasAttributes.php(607): Illuminate\Support\Str::studly('configuration_v...')
#7 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Concerns/HasAttributes.php(2082): Illuminate\Database\Eloquent\Model->hasGetMutator('configuration_v...')
#8 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Concerns/HasAttributes.php(492): Illuminate\Database\Eloquent\Model->transformModelValue('configuration_v...', '')
#9 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Concerns/HasAttributes.php(446): Illuminate\Database\Eloquent\Model->getAttributeValue('configuration_v...')
#10 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Model.php(2260): Illuminate\Database\Eloquent\Model->getAttribute('configuration_v...')
#11 /home/soldiers/public_html/dev-2025/laravel/app/Models/Configuration.php(26): Illuminate\Database\Eloquent\Model->offsetGet('configuration_v...')
#12 /home/soldiers/public_html/dev-2025/includes/init_includes/init_db_config_read.php(19): App\Models\Configuration->loadConfigSettings()
#13 /home/soldiers/public_html/dev-2025/includes/autoload_func.php(40): require_once('/home/soldiers/...')
#14 /home/soldiers/public_html/dev-2025/includes/application_top.php(329): require('/home/soldiers/...')
#15 /home/soldiers/public_html/dev-2025/index.php(25): require('/home/soldiers/...')
#16 {main}
thrown in /home/soldiers/public_html/dev-2025/laravel/vendor/symfony/polyfill-mbstring/Mbstring.php on line 667

Don Wagner:

Did a clean Install of Zen Cart 2.1.0 (PHP Level ea-php83), in its own subdomain (production is in another subdomain running PHP Level ea-php72). Installation completed with just a warning "PHP GZip extension not detected. ... Your hosting company can take care of this for you.". Hosting company response was "PHP Gzip should be enabled at the moment, I have as well tested through PHP script and seems to be working as intended." So I continued.

Installation successfully completed; however, I get a 500 Fatal Error attempting to access both the storefront and admin. I admit I'm in over in over my head but would really like to see this through.

Most profuse thanks in advance for any assistance you can provide.

Error log:

[22-Jan-2026 17:08:29 UTC] PHP Fatal error: Uncaught Error: Call to undefined function Symfony\Polyfill\Mbstringiconv_substr/COLOR in /home/soldiers/public_html/dev-2025/laravel/vendor/symfony/polyfill-mbstring/Mbstring.php:667
Stack trace:
#0 /home/soldiers/public_html/dev-2025/laravel/vendor/symfony/polyfill-mbstring/bootstrap80.php(72): Symfony\Polyfill\Mbstring\Mbstring::mb_substr('configuration', 0, 1, 'UTF-8')
#1 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/support/Str.php(1135): mb_substr('configuration', 0, 1, 'UTF-8')
#2 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/support/Str.php(1205): Illuminate\Support\Str::substr('configuration', 0, 1)
#3 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/support/Str.php(1119): Illuminate\Support\Str::ucfirst('configuration')
#4 [internal function]: Illuminate\Support\Str::Illuminate\Support{closure}('configuration')
#5 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/support/Str.php(1119): array_map(Object(Closure), Array)
#6 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Concerns/HasAttributes.php(607): Illuminate\Support\Str::studly('configuration_v...')
#7 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Concerns/HasAttributes.php(2082): Illuminate\Database\Eloquent\Model->hasGetMutator('configuration_v...')
#8 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Concerns/HasAttributes.php(492): Illuminate\Database\Eloquent\Model->transformModelValue('configuration_v...', '')
#9 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Concerns/HasAttributes.php(446): Illuminate\Database\Eloquent\Model->getAttributeValue('configuration_v...')
#10 /home/soldiers/public_html/dev-2025/laravel/vendor/illuminate/database/Eloquent/Model.php(2260): Illuminate\Database\Eloquent\Model->getAttribute('configuration_v...')
#11 /home/soldiers/public_html/dev-2025/laravel/app/Models/Configuration.php(26): Illuminate\Database\Eloquent\Model->offsetGet('configuration_v...')
#12 /home/soldiers/public_html/dev-2025/includes/init_includes/init_db_config_read.php(19): App\Models\Configuration->loadConfigSettings()
#13 /home/soldiers/public_html/dev-2025/includes/autoload_func.php(40): require_once('/home/soldiers/...')
#14 /home/soldiers/public_html/dev-2025/includes/application_top.php(329): require('/home/soldiers/...')
#15 /home/soldiers/public_html/dev-2025/index.php(25): require('/home/soldiers/...')
#16 {main}
thrown in /home/soldiers/public_html/dev-2025/laravel/vendor/symfony/polyfill-mbstring/Mbstring.php on line 667
See the docs for the server requirements: https://docs.zen-cart.com/user/first_steps/server_requirements/#php-extensionsmodules-used-by-zen-cart

Specifically, it appears that your site's PHP 8.3 load doesn't include the [COLOR=#ff0000]**iconv **extension. Your hosting company should be able to help.

I went to another domain of mine which hosts an old static HTML site (no PHP apps), created a SQL databse, set PHP to 8.3, and ran the Install. Everything went fine with no warnings. All the required PHP extensions were already enabled, including iconv which was greyed out and couldn't be turned off even if I wanted. So guessing the domain running my Zen Cart store in production was not really a proper environment for a "clean" install due to various fiddling I'd done in the past.

So am now going to replace the new table data with my old production data, and run a 2.1.0 upgrade as opposed to clean install. Then, install the 2.1.0 version of the template I've been using (Fluorspar), and make some custom changes.

If that plan doesn't sound right to you, please let me know. I recognized you immediately as the Software Guy whose advice I have been following for years. Kudos to you!