/wp-admin/admin-ajax.php the server responded with a status of 500 ()

Hi! How are you? Bassically I would like this plugin to work with my site but I am having this problem when i Try to send a invitation, here I copy the error:

write(4, “[17-Mar-2017 03:33:23 UTC] PHP Fatal error: Uncaught exception ‘phpmailerException’ with message ‘Invalid address: ‘ in /wp-includes/class-phpmailer.php:946\nStack trace:\n#0 /wp-includes/pluggable.php(352): PHPMailer->setFrom(NULL, ‘Transfer Securi…’)\n#1 /wp-content/plugins/upme-invitation-codes/classes/class-upme-inc-manager.php(231): wp_mail(‘wordpress@trans…’, ‘Invitation for …’, ‘Your are invite…’, Array)\n#2 [internal function]: UPME_INC_Manager->send_invitation_codes(”)\n#3 /wp-includes/plugin.php(524): call_user_func_array(Array, Array)\n#4 /wp-admin/admin-ajax.php(92): do_action(‘wp_ajax_upme_in…’)\n#5 {main}\n thrown in /wp-includes/class-phpmailer.php on line 946\n”, 983) = 983
close(4) = 0
chdir(“/wp-admin”) = 0
setitimer(ITIMER_PROF, {it_interval={0, 0}, it_value={0, 0}}, NULL) = 0
write(1, “Status: 500 Internal Server Error\r\n”, 35) = 35