Authorize.net transactions all fail

[semboku]

We're using 2.1 CE and authorize.net sandbox account and all orders are failing. We're using Porto theme but it also fails in Luma. Authorize.net shows successful transactions on their end, but the Magento user gets the attached error and thinks the order failed. The spinner just keeps spinning and the page never moves on. The orders show up in Magento admin sales/orders as pending... but the user gets the error. Any ideas?

I have also attached my settings. 

[ShoaibRehman89]

@semboku

Your first point to troubleshoot the issue is AUTHORIZE.NET log file in var/log directory. They normally give you the error code as well so you can easily track the issue. 

I hope this answers your question. 

[sixgun]

My Mage 2.3.1 site is not generating this file - how do I enable it..   I've enabled everything I am familiar with - was this feature eliminated - if so how are we ever able to troubleshoot this crap interface... ?