Nowadays everybody recieves a lot of spams and to make our invite more trustful you can put the username on the subject avoiding also the reciever to delete it right away without reading it. Check below how to add the username in the subject:

The subject text is changed in your language ini file (en-GB.com_alphauserpoints.ini) at AUP_YOUAREINVITEDTOREGISTERON, but it is also definied in the controler.php file at yoursite/components/com_alphauserpoints. If you check the line 480 you will find the order it is defined at:

$subject = JText::_('AUP_YOUAREINVITEDTOREGISTERON' ) . " " . $SiteName;

So, let's suppose you want to put in the subject the name of the inviter and the text, just replace the code above (at line 480) as it:

$subject = $sender .  "  " . JText::_('AUP_YOUAREINVITEDTOREGISTERON' ) . " " . $SiteName;