To get Fedex working with PluginHive’s WooCommerce Shipping Services I divided the day between working with my client to confirm settings in WooCommerce and WSS, time in emails with PluginHive technical support (they are excellent), and a very lengthy phone call with a very helpful person at Fedex technical support. What I learned was that none of this will work until you submit two paper forms to Fedex and wait two days. Oh, and there could be a difference between the billing address Fedex shows in your profile and what the Revenue Department has on file.
So you want to be a programmer? Some days there is no code and all navigating bureaucracy to get to the one person who knows the correct checkbox to check.