Hello Cameron,
What do you see for usage on that key when you sign in at the Bing Maps Portal? See the steps here: https://learn.microsoft.com/en-us/bingmaps/getting-started/bing-maps-dev-center-help/understanding-bing-maps-transactions
Unfortunately, you will have to contact ESRI for support on setting up ARCMap but some simple issues might be that you put a space in front of the key or missed the final character
If the issue is that the imagery you are requesting is not available under a basic license, you can contact the Bing Maps Licensing team at MapLic@Microsoft.com to upgrade to Enterprise or if ESRI indicates there is an issue with your account, you can reach out to the Bing Maps Account team at MPNet@Microsoft.com.
Sincerely,
IoTGirl