Hey mate, I spoke with my hosting support and they found that the issue was with the plugin not being compatible with the latest PHP.
Can you confirm this:
“This is more of your plugin compatibility issue with PHP version 8.2.
You had configured PHP version 8.2 for your cPanel which is not compatible with FluentCRM plugin. I had to downgrade the PHP version to 7.4 and it is now allowing to add the list in FluentCRM.
If you want to use PHP version 8.2, then you need to check with plugin support for PHP 8 compatibility.”