Hi @Dom Steward Greetings! Welcome to Microsoft Q&A forum. Thank you for posting this question here.
I have tested creating a new key using the Bing Maps Dev Center at https://www.bingmapsportal.com/ I could create the key without any issue. Please see the below key I have created for reference.
There might be an intermittent issue which could have prevented you from creating the keys. I appreciate it if you could recheck the portal and let us know if you can generate the keys now.