What version of cPanel are you running? 11.25.0? 11.25.1?
If you're running 11.25.1, you may need to provide the literal database name.
ex:
Code:
$user = 'dave';
$result = $xmlapi->api1_query($user,'Mysql','adddb',array('adbname') ); //will create dave_adbname
$result = $xmlapi->api1_query($user,'Mysql','adduser',array('adbuser') ); //will create dave_adbuser
$result = $xmlapi->api1_query($user,'Mysql','adduserdb',array('dave_adbname','dave_adbuser','ALL') );
$result = $xmlapi->api2_query($user,'MysqlFE','userdbprivs', array('db'=>'dave_adbname','user'=>'dave_adbuser') );
Regards,
-DavidN