Authorize.net returning server error 500 while placing an order on magento 1.9

Question

I'm having an issue with Authorize.net since Jan 18th 2019. I'm getting server error 500 when placing an order one default Magento onepage checkout, also when placing an order from the admin section; I got white page with error 500.

I'm able to see the payment/transaction on authorize.net but not on Magento (No orders)

Other symptoms surfaced:

1. Some customers get a white screen page
2. Browser redirection to the Cart page without any error message
3. Empty error message
4. Invalid email address after placing an order
5. duplicate transactions
6. Customer registration are not stored in Magento DB after placing order.

What is the best approach to tackle such issue?

Answer 1

Authorize.net seems to be making some vaguely announced changes which may affect Magento.

If your customers see error message 'There was an error processing your order. Please contact us or try again later.'

and you have this in your exception.log:

Exception: Notice: Undefined offset: 1  in app/code/core/Mage/Paygate/Model/Authorizenet.php on line 1315

Then change

const RESPONSE_DELIM_CHAR = '(~)';

to:

const RESPONSE_DELIM_CHAR = '*';

This is covered here and on the authorize.net forums: Suddenly Auth.net payments are not getting saved in Magento with a fatal error on the checkout