Missing Orders with Opencart & Authorize.net

I have searched high and low and have tried a few solutions mentioned in the forum but none have worked. Nothing has solved my issue with orders going to missing orders even if they have been approved by Authorize.net. The user and admins are also not getting the emails to confirm their orders even though they have been approved.

I am using Version 1.5.6.4.

Thank you in advance for your help.