I tried to re-install the plugin and the theme, the same.
The solution that i found was to remove the $offer_id = NULL and 'i_offer_id' => $offer_id from ModelIIM.php file. But this made the plugin to work as it should, in the frontend, but still the emails are not sent.
This is the error_log that I have:
[26-Jan-2020 17:48:26 America/Indiana/Indianapolis] PHP Fatal error: Uncaught phpmailerException: Invalid address: (addAnAddress to): in /home/autodjpe/public_html/oc-includes/vendor/phpmailer/phpmailer/class.phpmailer.php:881
Stack trace:
#0 /home/autodjpe/public_html/oc-includes/vendor/phpmailer/phpmailer/class.phpmailer.php(821): PHPMailer->addOrEnqueueAnAddress('to', '', '')
#1 /home/autodjpe/public_html/oc-includes/osclass/utils.php(482): PHPMailer->addAddress('', NULL)
#2 /home/autodjpe/public_html/oc-content/plugins/backoffice_manager/email.php(168): osc_sendMail(Array)
#3 /home/autodjpe/public_html/oc-content/plugins/backoffice_manager/index.php(407): email_status(NULL)
#4 /home/autodjpe/public_html/oc-includes/osclass/classes/Plugins.php(42): bo_mgr_form_post(Array)
#5 /home/autodjpe/public_html/oc-includes/osclass/helpers/hPlugins.php(34): Plugins::runHook('posted_item', Array)
#6 /home/autodjpe/public_html/oc-includes/osclass/ItemActions.php(313): osc_run_hook('posted_item', Array)
#7 /home/autodjpe/public_html/oc-includes/osclass/controller/item.php(151): ItemAct in /home/autodjpe/public_html/oc-includes/vendor/phpmailer/phpmailer/class.phpmailer.php on line 881