I found this error was because the server my website was hosted on didn’t resolve the website’s DNS name locally. Therefore, when cUrl tried to visit a URL to create the databases, it was failing to visit the local server. Append these two lines immediately after “function zing_mailz_activate() {” on line 115 of the mailz.php file in the root of the plugin:
error_reporting(E_ALL);
ini_set('display_errors', '1');
If it is the same error, it will show you the URL which could not be resolved. You can visit this URL manually to create the tables in the database (hence the error when this is not done). Then retry activation and it should work.
(Sorry if this doesn’t make much sense, written in a hurry).