Authorized API send error on charge

Using this plugin, I was working with Authorize.net for over a year without any problems. For completely unrelated reasons, I needed to change the Transaction Key and API Signature Key for Authorize.net. The key updates in the Woocommerce > Settings > Payments > Authorize.net worked fine and the transactions go through the frontend of the website without any problems on the updates. I updated WooCommerce > Settings > Manual Payments > Authorize.net and updated the Transaction Key and Client Key (aka API Signature Key), and this plugin will no longer process Authorize.net transaction. I receive the following error:

“Sorry, the Login ID, Client Key, or both, are incorrect. Please check your settings and try again. Please also ensure that SandBox Mode is enabled or disabled according to your account type.”

The Sandbox account is NOT checked (because this is not a sandbox account and is actively processing payments). I have purged the caches on the host server a dozen times as well as on the PC. Nothing will get me past this error. This plugin will not apparently accept new Authorize.net Transaction and Client keys once they are entered into the system once. Can you assist on how to update these keys other than the WooCommerce > Settings > Manual Payments > Authorize.net menu because the keys do not appear to be updating.