ShipRush 11 FedEx - Ecommerce - WooCommerce

I had ShipRush working okay with WooCommerce on my website. Recently, I've found that ShipRush is no longer able to connect (ERROR: 33836B).

What I've done to try to fix the issue:
Downloaded the most recent PHP files (ShipRush_Plugin_for_WooCommerce_Build_4084849_Nov 21)
Uploaded the PHP files via FTP to the home directory of my website.
Generated a new 31 character access token. Generated new consumer key and consumer secret via the API tools of my WooCommerce installation.
Edited the ShippingZSettings.php to include the newly created access token, key and secret.
Deleted the old store and then created a new one. https://mysitename.net and the new access token.


Still, ShipRush cannot connect to my site (ERROR: 33836B).

Any suggestions as to what I might be doing wrong? How can I troubleshoot further?

Thanks