I recently did a complete rebuild/upgrade of my zen cart based site to v1.5.6c. The install went fine except for the integration of authorize.net. I have been using authorize.net (aim) since the beginning, probably 7 years or more, without issues. After the upgade to 1.5.6c I got a new transaction key and cancelled the old one. Still using the aim module I tested things out in sand box mode and all appeared ok. I next tried test mode and the credit card would not process. I got this error statement ...error 13 The merchant login ID or password is invalid or the account is inactive. I checked with authorize.net and my account is active. I tried manually processing a card through the authorize.net website and that worked ok. Authorize.net wanted to know why I was using aim as that was being phased out. So I activated the sim module with new transaction key and security key. Got the same error statement. I have no idea what is going on. I am about redy to try another gateway unless anyone has an answer for me.
Thanks in advance for any help!

url store.laurelmountainforge.com
php 7.2